RBR 750 dropping internet after lease expires, every 2-ish hours

I have an RBR750 (and two satellites that are currently disconnected to help with diagnostics) on xfinity.  Prior to this event, everything had been working fine with no drops for about a year.  We recently had work done in the neighborhood, which caused a 2-hour outage.  After this, my DHCP lease is only 2 hours long, and at the end of it, the internet stops working.  On the advanced -> connection status page, it looks like the lease has been renewed (with the same IP) after that 2-hour window, but the internet connectivity isn't there until I manually power cycle the modem.  If I catch it about 30 min prior to expiration, and do a release/renew (on the advanced->connection status page) it will continue functioning.  Doing just a renew (even if it appears to work by extending the time) immediately kills the internet as well.

I have tried replacing the modem (initially had a Docsis 3.0 Arris Surfboard, now a Docsis 3.1 Arris).  I have tried different routers.  One old router (linksys 1900 ACS) maintained a connection overnight, but this was before I realized it was related to DHCP leases, and I can't get it to replicate its success.  The linksys router was also previously used with xfinity, so my assumption is that it was recognized and got a longer lease.

Although I doubt this matters, while doing MRT ping/traceroute testing, I noticed that during the period when the linksys router was maintaining a connection, it's private IP (192.168.1.1) resolved to a comcast address personalcomputer.hsc1.comcast.wa or some such.  Any other time, it doesn't resolve to a name on traceroute testing.  I took this to mean that the comcast DNS server recognized the computer and had a long term lease for it, but I'm not a network professional.

Some version of this problem appears to have existed for a year or two now, but I haven't been able to find any suggestions to help.  The only person who seemed to have an effective strategy ended up downgrading their firmware.