After update to 3.0: error preparing SQL queries

[mzurborg-scopevisio]

Version:

• listmonk: 3.0 (updating from 2.5)
• OS: Debian 12

Description of the bug and steps to reproduce:
After updating the binary to 3.0 and running listmonk --config config.toml --upgrade which seems to successfully perform the migrations, listmonk starts successfully but only once.
http server started on 127.0.0.1:9642

Gracefully shutting listmonk down and running it again will however end up in the following error:
error preparing SQL queries: Error preparing query 'get-dashboard-charts': pq: prepared statement "1" already exists

Now it refuses to start anymore.

I've also tried reverting to a db backup and running the migrations in internal/migrations/v3.0.0.go manually, same start-up error.

Update: Forcefully closing all active db sessions via SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity WHERE pg_stat_activity.datname = 'listmonk' AND pid <> pg_backend_pid(); will allow listmonk to start again. But still, only once. Next start up, same error.

Most likely a db issue so I'll post db info as well:

Postgresql version: 14.12 (Debian 14.12-1.pgdg120+1)
listmonk user has grant all on listmonk db
DB runs via ssl verify-full with valid domain and cert

Update 2: OK found it out myself, db had a connection pooler in front of it which was configured in transaction mode. Listmonk only supports session mode, I changed it and now it works.

Closing ticket. Maybe people with similar problems will find this helpful info.