Why are my devices able to connect to some web-based programs but others time out?

This is a long and complicated story so I’ll try to be brief but detailed.

I live in an apartment building with about 80 units. We have a bulk Xfinity account that is included in our HOA. I work from home 4/5 days per week. We moved in 20 months ago and had no issues with Xfinity for the first 18 months.

In mid-December, my work computer (Dell desktop) began behaving strangely. I would be connected to the WiFi, with a strong signal, yet certain programs could not connect to the internet. The requests would time out. Yet, desktop apps like Teams and Outlook would work just fine. I resorted to using my old work laptop as a backup. Exact same thing.

My IT department investigated everything they could on my computers and found absolutely no reason why they shouldn’t be able to connect properly. My laptop would connect just fine if I brought it into the office. My desktop will work if I hotspot my phone. Neither worked if I hardwired them into the router with an Ethernet cable. All other devices in the household were working properly, except for some dropped connections with my smart home hub which I thought was unrelated.

After the holidays, I contacted Xfinity and got a tech out to have a look. He replaced the Xfinity router/modem to the upgraded XB8-T. He checked the security settings and there were no surprise firewalls in place. My desktop began connecting fully if I restarted it daily at the same time as the router, but would intermittently stop again.

Then it got worse. Nearly every device we have connected to the WiFi began experiencing the same issue. Browser-based activity would time out, some apps would fail to load, while others worked just fine. The issue would resolve as soon as we switched to cellular data.

I thought I could throw money at the problem and invested in an Orbi mesh system. But when I went to turn the Xfinity modem into bridge mode, I realized that our computers could not even load 10.0.0.1 while hardwired in. I was too scared to turn it into bridge mode if I couldn’t get it out.

Another tech came out. He checked all of the connections, saw no issues, and called his supervisor. The supervisor said he could see devices connecting and disconnecting at random on his end. Some devices that we knew were connected weren’t showing up at all, some that were powered off were showing as still online. But on paper, if the tech wasn’t there, it would have looked fine.

This was when they started taking it seriously. Shout out to Reggie if this gets back to him. Thank you. We tried a couple of other fixes- using 2.4 only and disconnecting a bunch of devices in case it was overloaded- same issue.  He put in a request to have the next level of tech come out.

So the next tech comes by. Replaces every single connection and every bit of line he could access all the way back to the junction box in our stairwell. He moved us to a different port. Replaced the moka. Everything. When he left, everything was working.

Monday of this week, I log on for work… same issue. I’ve ordered a different kind of Orbi that tech #3 said might work without having to put it in bridge mode. It’s coming tomorrow and I’m supposed to call him back.

I’m exhausted. My boss is telling me I will have to come into the office full time if I can’t get this resolved.

Does anyone have any idea what might be going on here? Why can the devices connect to some internet services but not others? Why is it random when things get kick off or allowed to connect fully? Heeeeeelllllpp meeeee