Replication sequence

Hi all,
I have two servers, a primary and a secondary one with a streaming replica
setup.
Today I noticed that some sequences are not lined-up, the replica ones are
well ahead, while the records number is the same. How is it possible?

Thanks,
Paolo

--
-- primary server
--
postgres(at)db-srv1:~$ psql
psql (9.5.19)
cf-db-srv1:5432 postgres(at)rete_llpp=# SELECT last_value FROM
bobo.menu_pages_mp_id_seq;
┌────────────┐
│ last_value │
├────────────┤
│ 74 │
└────────────┘
cf-db-srv1:5432 postgres(at)rete_llpp=# select count(*) from bobo.menu_pages;
┌───────┐
│ count │
├───────┤
│ 74 │
└───────┘

--
-- replica server
--
postgres(at)db-srv2:~$ psql
psql (9.5.24)
cf-db-srv2:5433 postgres(at)rete_llpp=# SELECT last_value FROM
bobo.menu_pages_mp_id_seq;
┌────────────┐
│ last_value │
├────────────┤
│ 105 │
└────────────┘
cf-db-srv2:5433 postgres(at)rete_llpp=# select count(*) from bobo.menu_pages;
┌───────┐
│ count │
├───────┤
│ 74 │
└───────┘