Final update: 2degrees sending me a FritzBox. The workaround did not work.

We turn our orbi off every night. Could be relevant

canterburydays: We turn our orbi off every night. Could be relevant

Don't do this. Routers are designed to stay on and there is absolutely no point turning them off every night. Routers are like computers, turning them off all the time can cause damage.

It sounds like this is part of the reasoning behind your problems.