Internet connection Heisenbug - Change provider?

I am on Telekom DSL, with the default Telekom router. The speed is great, but many times per day, it just randomly freezes for a few seconds/a minute. This is super annoying, but I cannot reliably check if the problem stops or not after any kind of solution.

I have replaced the router (with the same model), moved appartment (from old to old building), and I have not managed to get a technician to come to me, because I am always stuck at the first-level support, not being able to conclude if the problem was fixed or not by trivial solutions.

Is this a general issue with Telekom in Munich, or with some Telekom routers? Does any other company run their own network, or would changing the provider not help? Am I just unlucky with the building cables? A neighbor told me they had no issues with another provider.

I think that Fiber is not available in my building, while I have heard bad experiences with "Kabel" connections.