Dc issues. Not caused by PoE

This has been an ongoing problem but has never killed me so it was just annoying. It killed me today....

My internet restarts approximately every 45 minutes. Even when I'm not playing PoE. If I'm just watching Twitch it will reload the stream/chat randomly. The things that have changed that I know of since this has started happening is I got a new smart phone (connected to my network) and I got a new rented modem/router from my ISP. Any suggestions on what I could try to help me narrow down the problem?

My PC is wired.

Thanks in advance.

try a tool which permanently tests the availability of external websites like described here.

when you recognize your connection is broken, look at the tool: if your computer cannot reach your router or if the router is not sending the pakets outside your private network.

in either case afterwards you know where your problem is.