T25 keeps losing internet connection

I bought this house 2 years ago and I hired an installer to setup my wifi as I was moving from out of state and wanted things setup before I got here. Otherwise I consider myself very tech savvy as I was previously a network admin at a large international law firm, and I would have done the install myself. We have Xfinity here and he suggested outright purchasing a T25 modem instead of renting. Having previously owned a Surfboard modem when I was on Optimum for nearly 20 years and having almost no issues it, I said that would be fine.  It was working flawlessly up until about 2 months ago. I work from home and during business hours, I can not have down time. I use a PC and laptop, both of which are hardwired to a TP-Link Archer C5400. I had a 2nd Archer A20 hardwired to the C5400 operating as an access point. One day, suddenly, my entire house lost internet connectivity, nothing hardwired or wireless was able to connect to anything. I rebooted the C5400 thinking that was the issue but when it came back up, still nothing was working. I then cycled the power on the T25 and that worked. The same thing happened 3 more times over the last few weeks. Oddly, I am able to ping remote servers with no packet loss and the phones work (I have VoIP service as well) but nothing is able to connect. I’ve spoken to Xfinity when this happens and they don’t see anything wrong on their end and of course as part of their over-the-phone troubleshooting, they have me reboot the modem, which always fixes it. I don’t want them to send a tech out since I own the modem and if it is a problem with the modem, I get charged. This happened again at 6:30AM this morning (when my alarm system switches to cellular backup, it e-mails) and I woke up to no internet. Please help! The modem is still under warranty until 9/2023.