Swapped gateway (from Xb7 to Xb8) and now internet drops intermittently

Hello!   I had an Xb7 xfinity gateway that I'd had zero issues with for many years...in April, I was sent a new Xb8 since mine was outdated and a security risk.  The new one worked fine for about a day and then it started having intermittent dropouts...I tried to gather stats on when and what I was doing, but I couldn't find a pattern to it.  The chatbot said my service was fine, in the meantime, my internet comes and goes with no warning...wired and wifi...Finally in June I was able to get a tech to come out...he told me the new Xb8's were garbage and he swapped me back to one that looked like the older X7, but with the updates required.  He was on with tech support for a while and they finally got this thing to connect.  That lasted about a day...got a second tech out today who thought that I needed to separate my signals to specify the 2.4 vs 5.0 signals rather than use the auto select function (this used to be how my old was set up) but then he ended up swapping me back to a different Xb8 gateway, connected it up and off he went.  I had a steady connection for a few hours before the signal started dropping out again.  I do the "test internet" option on the xfinity app which tells me that I have anywhere between 29% of plan service and 105% of plan service.  ookla speed test shows that I typically have about 40 or 50Mbps in my basement via wifi...wired I'm at about 400.  Today when the tech left, ookla test at the gateway said I was at 900+.  I pay for gig service.  

If I'm having the same problem with 3 different gateways, I'm thinking the issue might be with how it's configured, not necessarily the hardware itself.  Zero issues for years until the new gateway, now I'm on modem #3 since the end of April and still having dropouts...can someone help me figure this out or tell me how to escalate this to a higher level tech that can do some actual troubleshooting.  

Thank you!