One of my customers has an issue with logical replication. As $SUBJECT says, multiple table synchronization happens serially. To be honest, it doesn't do this every time. It happens when the tables are big enough.
Attached is a small test case where it still happens for me on 12.6, 11.11, and 10.16. I can't make it happen on 13.2. I don't know why. It may imply bigger tables for 13.2, but why? I simply don't know.