On a dockerized CI environment (Ubuntu 20.04) we are getting the following error:

cd dev/tests/integration; ../../../vendor/bin/phpunit -v --testsuite 'Our Tests'

...

Disabling Maintenance Mode:

In ResourceConnection.php line 148:

[DomainException]
Connection "default" is not defined

This seems during the automated sandbox installation.

When we run the command again, it works.

But after we deleted the sandboxes using

rm dev/tests/integration/tmp/sandbox-* -r

it does not work again on the first try.

We found https://github.com/magento/magento2/issues/22198 which says this could be related to the opcache.enable_cli option, but this one is already switched to Off.

Does anybody know how to fix this?

It did not happen for Magento 2.4.2 and surfaced after the upgrade to Magento 2.4.3.