There is publisher and subscriber logs, but the logs on both nodes did not give me clarity.
Master (time when errors start to appear):
 
2024-03-28 22:26:08.459 +07 [1004642] ERROR:  could not start WAL streaming: ERROR:  replication slot "pg_975006_sync_972467_7293549148661379912" does not exist
2024-03-28 22:26:08.462 +07 [1597281] LOG:  background worker "logical replication worker" (PID 1004642) exited with exit code 1
2024-03-28 22:26:08.466 +07 [1048261] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "scan_type_i18n" has started
2024-03-28 22:26:08.542 +07 [1048261] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "scan_type_i18n" has finished
2024-03-28 22:26:08.548 +07 [1048263] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "phone_type_i18n" has started
2024-03-28 22:26:08.641 +07 [1048263] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "phone_type_i18n" has finished
2024-03-28 22:26:08.644 +07 [1048264] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "reply_status_type_i18n" has started
2024-03-28 22:26:08.690 +07 [1048264] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "reply_status_type_i18n" has finished
2024-03-28 22:26:08.693 +07 [1048265] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "user" has started
2024-03-28 22:26:09.054 +07 [1048265] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "user" has finished
2024-03-28 22:26:09.059 +07 [1048267] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "queue_event" has started
2024-03-28 22:26:09.141 +07 [1048267] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "queue_event" has finished
2024-03-28 22:26:09.146 +07 [1048274] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "credit" has started
2024-03-28 22:26:09.163 +07 [1048274] ERROR:  could not start WAL streaming: ERROR:  replication slot "pg_975006_sync_972243_7293549148661379912" does not exist
2024-03-28 22:26:09.165 +07 [1597281] LOG:  background worker "logical replication worker" (PID 1048274) exited with exit code 1
2024-03-28 22:26:09.167 +07 [1048281] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "requisite_value_contragent" has started
2024-03-28 22:26:09.184 +07 [1048281] ERROR:  could not start WAL streaming: ERROR:  replication slot "pg_975006_sync_972563_7293549148661379912" does not exist
2024-03-28 22:26:09.186 +07 [1597281] LOG:  background worker "logical replication worker" (PID 1048281) exited with exit code 1
2024-03-28 22:26:09.189 +07 [1048282] LOG:  logical replication table synchronization worker for subscription "log_rep_sub", table "order_registry_np" has started
 
The same time on replica:
 
2024-03-28 22:26:07.967 +07 [25424] postgres@claims LOG:  duration: 2406278.201 ms  statement: COPY public.orders (id, order_number, order_date, order_amount, payment_info_code, payer_code, payer_name, receiver_code, receiver_name, sender_code, sender_name, cargo_description, cargo_volume_weight, cargo_weight, declared_price, currency_code, internet_store_number, subdivision_code, cfo_code, active, date_created, date_updated, delay) TO STDOUT
2024-03-28 22:26:08.426 +07 [25424] postgres@claims ERROR:  replication slot "pg_975006_sync_972467_7293549148661379912" does not exist
2024-03-28 22:26:08.466 +07 [1170] postgres@claims LOG:  logical decoding found initial starting point at B1C5/BFBA3410
2024-03-28 22:26:08.466 +07 [1170] postgres@claims DETAIL:  Waiting for transactions (approximately 1) older than 2998665818 to end.
2024-03-28 22:26:08.469 +07 [1165] [unknown]@[unknown] LOG:  could not accept SSL connection: EOF detected
2024-03-28 22:26:08.496 +07 [1170] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBA4580
2024-03-28 22:26:08.496 +07 [1170] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:08.507 +07 [1170] postgres@claims LOG:  starting logical decoding for slot "pg_975006_sync_971138_7293549148661379912"
2024-03-28 22:26:08.507 +07 [1170] postgres@claims DETAIL:  Streaming transactions committing after B1C5/BFBA45B8, reading WAL from B1C5/BFBA3290.
2024-03-28 22:26:08.507 +07 [1170] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBA3410
2024-03-28 22:26:08.507 +07 [1170] postgres@claims DETAIL:  Logical decoding will begin using saved snapshot.
2024-03-28 22:26:08.546 +07 [1172] postgres@claims LOG:  logical decoding found initial starting point at B1C5/BFBAA200
2024-03-28 22:26:08.546 +07 [1172] postgres@claims DETAIL:  Waiting for transactions (approximately 2) older than 2998665822 to end.
2024-03-28 22:26:08.594 +07 [1172] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBB5E80
2024-03-28 22:26:08.594 +07 [1172] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:08.602 +07 [1172] postgres@claims LOG:  starting logical decoding for slot "pg_975006_sync_970776_7293549148661379912"
2024-03-28 22:26:08.602 +07 [1172] postgres@claims DETAIL:  Streaming transactions committing after B1C5/BFBB5EB8, reading WAL from B1C5/BFBA5290.
2024-03-28 22:26:08.602 +07 [1172] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBAA200
2024-03-28 22:26:08.602 +07 [1172] postgres@claims DETAIL:  Logical decoding will begin using saved snapshot.
2024-03-28 22:26:08.645 +07 [1173] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBB8E28
2024-03-28 22:26:08.645 +07 [1173] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:08.652 +07 [1173] postgres@claims LOG:  starting logical decoding for slot "pg_975006_sync_971808_7293549148661379912"
2024-03-28 22:26:08.652 +07 [1173] postgres@claims DETAIL:  Streaming transactions committing after B1C5/BFBB8E60, reading WAL from B1C5/BFBB8E28.
2024-03-28 22:26:08.652 +07 [1173] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBB8E28
2024-03-28 22:26:08.652 +07 [1173] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:08.697 +07 [1174] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBBE588
2024-03-28 22:26:08.697 +07 [1174] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:09.019 +07 [1174] postgres@claims LOG:  starting logical decoding for slot "pg_975006_sync_971995_7293549148661379912"
2024-03-28 22:26:09.019 +07 [1174] postgres@claims DETAIL:  Streaming transactions committing after B1C5/BFBBE5C0, reading WAL from B1C5/BFBBE588.
2024-03-28 22:26:09.019 +07 [1174] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBBE588
2024-03-28 22:26:09.019 +07 [1174] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:09.056 +07 [1180] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBE0C88
2024-03-28 22:26:09.056 +07 [1180] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:09.105 +07 [1180] postgres@claims LOG:  starting logical decoding for slot "pg_975006_sync_972492_7293549148661379912"
2024-03-28 22:26:09.105 +07 [1180] postgres@claims DETAIL:  Streaming transactions committing after B1C5/BFBE0CC0, reading WAL from B1C5/BFBE0C88.
2024-03-28 22:26:09.105 +07 [1180] postgres@claims LOG:  logical decoding found consistent point at B1C5/BFBE0C88
2024-03-28 22:26:09.105 +07 [1180] postgres@claims DETAIL:  There are no running transactions.
2024-03-28 22:26:09.129 +07 [1181] postgres@claims ERROR:  replication slot "pg_975006_sync_972243_7293549148661379912" does not exist
2024-03-28 22:26:09.151 +07 [1182] postgres@claims ERROR:  replication slot "pg_975006_sync_972563_7293549148661379912" does not exist
2024-03-28 22:26:09.172 +07 [1184] postgres@claims ERROR:  replication slot "pg_975006_sync_972454_7293549148661379912" does not exist
2024-03-28 22:26:09.196 +07 [1185] postgres@claims ERROR:  replication slot "pg_975006_sync_972467_7293549148661379912" does not exist
 
 
28.03.2024, 20:03, "David G. Johnston" <david.g.johnston@gmail.com>:
On Thu, Mar 28, 2024 at 9:59 AM PG Bug reporting form <noreply@postgresql.org> wrote:
The following bug has been logged on the website:

Bug reference:      18415
Logged by:          Andy Kosheen
Email address:      koderan@yandex.ru
PostgreSQL version: 15.4
Operating system:   Oracle Linux Server 8.4
Description:       

In the process of logical replication from version 13.3 (on Ubuntu 16.04.6
LTS) to version 15.4 (on Oracle Linux Server 8.4), when most of the data has
already been transferred, the following errors begin to occur, appearing
endlessly until you stop the replication process (this situation occurs on
databases larger than at least 50GB, even if there is a small number of
transactions on the source database):
2024-03-20 03:19:41.410 +07 [3433858] LOG:  logical replication apply worker
for subscription "log_rep_sub" has started
2024-03-20 03:19:41.425 +07 [3433858] ERROR:  could not start WAL streaming:
ERROR:  replication slot "log_rep_sub" does not exist
 
 
Suggest you check the publisher logs and see why the replication slot went away.
 
David J.