Downloads on Xbox Series X drop to 0 Mbps

So, I’ve been dealing with this issue for about a month now. It sorta started out of nowhere, where one day I noticed my games not launching after hitting launch. Either they were delayed to launch or just wouldn’t launch at all for a good long while. Then, I also saw that my downloads began dropping to 0 Mbps. Sometimes downloads would go at full speed like normal for about 10 min before dropping to 0, other times they’d go for only 20ish seconds before dropping to 0. Either way, they were dropping at some point.

At first I tried doing all the troubleshooting stuff… hard resetting, factory resetting, clearing cache, doing port forwarding stuff, changing the DNS, etc. Basically everything a normal person would do. Usually whenever I hard reset my Xbox and/or the modem, it’ll download smoothly for a reasonable amount of time before inevitably dropping to 0. Sometimes after dropping to 0, it’ll go back to normal for a short period of time before dropping again. So I can still download games eventually, but it’s obviously really annoying.

I tried connecting my cousin’s Xbox to my WiFi just to see if it would drop to 0 on her’s, and it did, which made me think it’s not on the Xbox side.

Btw, this has been happening both on WiFi and Ethernet cable.

So after that, I was talking to my ISP, which is Xfinity, and they came out and replaced my modem, which did nothing. The tech spent some time here doing everything he knew to do and couldn’t fix the issue. Then, I contacted them again because at that point I was convinced it had to be on the infrastructure side of things, since my cousin’s Xbox had also dropped downloads only on my WiFi. Plus, the downloads don’t drop on Xfinity’s hotspot, even though it’s super slow it didn’t drop. So I was totally convinced it wasn’t on my end. Then, the tech came out again with his supervisor and network guy, and all their tests showed everything was working fine, and they wanted to see what my Xbox was doing, so I showed them and they were pretty dumbfounded. Said they had never seen this sorta issue before.

Anyway, their plan was to give me an even better modem, which they returned and set up a couple days after that, and of course the issue still existed. So the downloads dropping to 0 has persisted across three different modems now at this point. I’m still convinced it’s on their infrastructure side, or something somewhere. I don’t know enough about the inner workings of the internet.

So I honestly have no idea where to go from here. Any help would be appreciated. Also, I’ve read it could have something to do with the IPv6, but Xfinity’s modems don’t let you turn that off, nor do I think you can disable it on the Xbox either. But I’m just really at a loss here. I’ve been with Xfinity for years now and have never encountered this issue before. So yeah, that’s basically where I’m at.