Pooling issue with postgres

[Wardormeur]

From Logentries:
TimeoutError: Knex: Timeout acquiring a connection. The pool is probably full. Are you missing a .transacting(trx) call (https://github.com/tgriesser/knex/blob/46dbe917d7cbc1748aba2ee9050dafea0b840fc0/src/client.js#L311) , which happens every ~2 minutes.
We don't use directly knex, but bookshelf, which makes use of knex.
The error happens when the pool, handled by tar, doesn't return a valid connection. However, pg connections rarely go over 2 (for 2 pods), and AWS doesn't report any connection issue.
The default configuration for knex is { min: 2, max: 10 }, yet never reaches it (https://knexjs.org/#Installation-pooling). Increasing it had not effect.

[Wardormeur]

Upgrading the version of bookshelf didn't fix it.

[Wardormeur]

Activating the logging of transactions doesn't log anything, despite the error message.
Clueless, I leave it to the curious for next year.