Service hangs with "Failed to load storage mapping from database"

[solracsf]

Sometimes, i can't find the root cause, i get this in the syslog after several days of normal running:

ERROR [notify_push] src/lib.rs:154: Failed to load storage mapping from database: pool timed out while waiting for an open connection

or

WARN [notify_push::connection] src/connection.rs:54: Invalid credentials

or

WARN [notify_push::connection] src/connection.rs:54: Socket error during authentication

I've read https://github.com/nextcloud/notify_push/issues/29 but this is not at the first connection, but while running (i'm indeed using localhost to force socket connection at /var/run/mysqld/mysqld.sock).

But at the same time:

php occ notify_push:self-test
✓ redis is configured
✓ push server is receiving redis messages
✓ push server can load mount info from database
✓ push server can connect to the Nextcloud server
✓ push server is a trusted proxy
✓ push server is running the same version as the app

configuration is:

'redis' =>
array (
  'host' => '10.91.135.191',
  'port' => 6379,
  'dbindex' => 5,
  'timeout' => 0,
),
'dbtype' => 'mysql',
'dbhost' => 'localhost',