Android Client stops updating position?

I have two Android phones set to update their position every 5mins.
They are registered on the Server fine, there are no errors in the app.
They have permissions to the GPS, but after a random amount of time they both stop sending their position.
The services are running and do not crash.

Only way to update is to open the app, then it sends its position with in a few seconds and I see the latest position on the Server/Manager.
I see no errors in the app log, just big gaps between 'location update' (e.g. 30min) when it should be 5mins.
I have read the troubleshooting page, its says to check server address which is fine.

So summary - no errors, system works fine, but updates do not auto send every 5mins, as if the apps sleeps?
Any ideas where to look?

Have you added apps to battery optimisation exceptions?

I have set app: Battery optimization - Not optimized.
Will test for an hour.

Thanks Anton, updating every 5mins now, that was the setting to change.