Arris S34 with 2GB service

I upgraded 1200 MB and 35 MB up Internet to 2000MB down and 250MB up two weeks ago. As I had Arris S33 modem, I decided to replace it right away with Arris S34 modem. I used the self-activation for the new modem. Everything worked fine for a week (I was getting 2300 MB down and 300 MB up). This is impressing.

After a week, the down speeds started to go down to something like 80 MB. Various speed tests showed the speed hand "freezing" (staying at the same value) and some websites or apps started to freeze at the same time.

A S34 cable modem reboot typically solved the issue.

Decided to chat with an Xfinity agent and was told that my account was still showing the old speed, so he adjusted it. He also dispatched the new boot file to the modem. and the modem was rebooted afterwards. Everything went back to the high speeds of 2300/300 mb (for a few hours). And back to up speeds of about 80 mb. A cable modem reboot fixed it again for a few hours.

My Internet speeds were identical all the time (before the up upgrade to 2GB) at 1300 MB down and 40 MB up. I did not change any networking components - I have my network set to 2.5GB and everything matches. Two of my Windows 11 computers have 2.5 GB Ethernet connections. I have four WiFi 7 ceiling access points connected via 2.5 GB Ethernet cables. Both wired and wireless speeds are impacted.

Any suggestion what else can be done for my case of Arris S34 with the 2GB Internet?