Some examples:
1. I've seen a delay of hours without any messages being sent on the replication protocol, likely due to a large transaction in the WAL not committed when running out of disk space.
2. `PgError.58P02: could not create file \"pg_replslot/<slot_name>/state.tmp\": File exists`
3. `replication slot "..." is active for PID ...`, with some system process holding on to the replication slot.
4. `can no longer get changes from replication slot "<slot_name>". ... This slot has never previously reserved WAL, or it has been invalidated`.
All of these require manual intervention on the server to resolve.
And that's not even taking into account HA/failover, these are just issues with logical replication on a single node. It's still a great feature though, and often worth having to deal with these issues now and then.