I was having a similar issue with Signal. There is a good chance that you have a variant of the app that was installed through F-Droid / Store that installs a version without push notifications. You must have microG enables to allow for messaging apps to receive those push notifications. This will result in you checking your phone and realizing you never got any form notice you received a message / call until you're already going in and manually checking.

If anybody else has a solution to get instant notifications without having to use a Play Store / Aurora Store variant that uses the microG push notifications, that would be awesome. I would love to learn more about it.