New ISP - now RBR40 loses internet constantly

Community,  I need your input.   I had to switch to a new ISP recently due to a change to my prior ISP that was giving me poor Mbps on 5G due to tower locations.   I had no issues for the past 8 years with the RBR40 getting an internet signal.    Now, I have a Charter Spectrum modem which is a basic modem only EU2251 (no router combo).    I figured no problem and easy install for the tech.    But, it's been about 16 hours since the install yesterday, and the RBR40 just drops internet constantly like every ten minutes, and even when I do have it,  I get buffering.    The testing of the speed on the Orbi admin shows download and upload speeds in the hundreds well above anything I've had historically.  

I have reviewed recommendations, made slight modifications, switched out a 5e cable with a 6, and even updated the latest and last firmware update 2.7.6.6 that I found.    Nothing is working.    I know RBR40 is old and only Wifi5, but I can't believe that a basic Spectrum modem would give RBR40 this many issues that it can't stay connected.   I've removed power from both and restarted them in sequence of the modem fully online , then powered on the RBR40 multiple times.    Everything looks good, and then bam,  internet stops.   It comes back about two minutes later, and the process repeats.

I do plan on calling Spectrum today.    I don't feel I should need to get a new mesh system just for a new internet provider with a basic modem.    Any recommendations?