Question about Zyxel NR7101 5G

I have been using the thing for a few days now. Unfortunately, the router hangs up at some point. Firstly, the connection slows down and secondly, there are longer interruptions and even total failure. When I restart, I get speeds of 500 Mbps down and 150 up again. But eventually it drops down to 4G until the thing hangs up again. Most of the time this happens within 12 hours. Does anyone know what could be causing this? Could there theoretically be a new firmware or something? I rule out throttling by the ISP, because after every restart it has wonderful 5G speeds again.