DOCSIS3.0 is slow but consistent while DOCSIS3.1 is faster but fails often

I have Xfinity high speed service in the SF Bay Area and have been frustrated with the following issue. My OLD Netgear CM600 (DOCSIS3.0) works well and is stable, but limits my connection speeds due to the age of the modem. I've tried 2 different DOCSIS3.1 models (Netgear CM1200 and Motorola MB8611) and both have the same problem. They both connect and provide higher speeds BUT disconnect/reconnect randomly (several times a day) resulting in no internet for 5 minutes. I've had an Xfinity technician come out and re-wire the cable coming into the house. We still have the same issue. 

This post from a couple of years ago captures what we have been experiencing since establishing service: https://forums.xfinity.com/conversations/your-home-network/docsis30-works-31-no-longer-functional/605f901fc264e93e85820b74.

Is there a known functional issue for Xfinity and DOCSIS3.1? Is there anyone who is successfully maintaining a stable connection with DOCSIS3.1 modems? I briefly owned an Aris SB8200 but returned it when the technician told me there was a known issue that Aris and Xfinity were working to resolve. Could this be more widespread? For such a critical service, I'd like a clearer explanation of what the problem is and how it can be resolved. Most support focuses on the "did you make sure your modem is plugged in or please manually restart your modem" level, which hasn't been helpful.