Internet dropping even after upgrade

Good morning,

Over the past month my internet service has been randomly dropping.  By dropping I mean losing service several times an hour.  I initially thought it was the modem (I had a Arris SB8200).  I was on the 800mbps plan.  It would be fine and working great, then just drop service.  This is on all devices wired and wireless.  I did some testing, disconnected my router and connected my pc directly to the modem.  This still resulted in drops.  I tried several times working with Xfinity assistant (not helpful at all).  Everything pointed to a bad modem.  I had checked all my connections to make sure it was tight.  I have one line coming into my house, no splitters.   I decided to replace the modem.

I bought a Arris S34 to be ahead of the curve and upgraded my service to the 1.2 gig plan.  This changed nothing.  The online tech stated the line coming into my house was good.  They told me I need a service call.  Tech came out to the house.  He replaced the cable ends noting they were old and not something Comcast uses (although it was installed by Comcast years ago).  He had some of the same issues I had initially.  After he replaced the cable ends the service improved.  He blamed my issue on my router.  So of course, I bought a new router.

I now have a TP-Link BE63 Mesh system.  Just two pods, my house isn't that big.  The speed is amazing!!!   I am getting download speeds at 1.2 gig download and around 38 mbps upload.  Outstanding!!!! Service will be fine then it drops off just like before.  I still have buffering issues on my devices.  TP-Link has a Deco app that you can actually check on your service when you are out of your network.  The network is down a lot. I have been checking from time to time when I am at work.  Buffering issues last night trying to watch my Roku was an issue.  Every time I try to run a speedtest to see what is going on, the service comes back up.  

I am looking for any advice you can give at this point.  I don't want to necessarily have another tech come out.   This last one was not the brightest, I had to help him with a few things when he couldn't get things running.  What do you need from me? Event logs from the router and modem?  I am just really frustrated at this point.

Thank you for your assistance in advance.

Charlene

P.S. I also replaced ethernet cables as that was the very first thing the assistant suggests.  The coax cable was not swapped out because the tech noted that the speed was great coming through the line.