logical replication on 12.2: failed to increase restart lsn:

I try to replace a physical by a logical replication and get:
- - -
"serializing snapshot to pg_logical/snapshots/215-746C7C20.snap",,,,,,,,,"meteo"
"updated xmin: 1 restart: 0",,,,,,,,,"meteo"
"failed to increase restart lsn: proposed 215/746C7C20, after 215/746C7C20, current candidate 215/746C7C20, current after 215/746C7C20, flushed up to 215/746C7C20",,,,,,,,,eteo"
- - -
My understanding is, that initial catch up of existing table contents is done auromatically.

Related config on both ends is minimalistic:

publisher:
wal_keep_segments = 400 #!# 6GB in logfile segments, 16MB each; 0 disables
wal_level = logical
hot_standby_feedback = on

subscriber:
wal_keep_segments = 400 #!# 6GB in logfile segments, 16MB each; 0 disables
wal_level = logical
hot_standby_feedback = on

Anny help appreciated,
Axel
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PGP-Key: CDE74120 ☀ computing @ chaos claudius