Due to that VPNFILTER infection I put up a PSA at https://www.cnet.com/forums/discussions/this-just-in-reboot-your-internet-modems-and-routers/
The symptoms sound like what could happen and the timeframe is from then to now.
If not try one last idea before the ISP call. Set the DNS entry in your PC to 188.8.131.52 ir 4..2.2.1 and retest.
A few weeks ago I started having a problem with my internet connection. Whenever I first turn my computer on I have to restart my modem to connect to the internet at all. After that I have periods of time that last anywhere from 1-10 minutes where I cannot connect to anything new. If I'm already connected to something, an online game, discord, a stream, etc I don't see any interruptions, but I cannot open anything new. This happens constantly throughout the day. I'm hardwired through Ethernet, and the lights on both ports have changed since this started. My computers port went from green and yellow If I remember correctly to a solid red and blinking yellow. The modems port now has a solid orange/red for my Ethernet cable only. I've tried a different Ethernet cable with no success and I've tried the other modem ports. This specific problem seems to only be affecting my computer. It seemed like a motherboard problem to me but the other devices in my house supported by my ISP, mainly TVs, started having problems at the same time so I'll be calling them in the upcoming days too. Any advice is appreciated and I can provide more information if needed.