I need support with home internet connection, please

I am having a persistent problem with my home internet connection, specifically when attending Zoom calls.  I pay for gigspeed internet from Comcast, and while I never get that on my PC that is connected via a Cat 7 cable directly to the XB8 router, I get decent speed of between 187MBps download/102MBps median upload (based upon speed tests I have configured to run every 10 minutes for the past few days).  The PC I work off of it all of 10 feet from the Comcast XB8.  Wireless is similar speed.  Latency tests are all over the map, which is where I think my issue may lie.   

Specifically, my picture freezes occasionally on Zoom calls from my home network, and sometimes the internet access itself drops for a second or two, which I note because of the icon changes from the network connection to a globe in the system tray at the lower left of my PC.  I will also get messages intermittently from Zoom saying my connection is poor while on calls.  This all started a few months ago, after Xfinity was "upgraded" in my neighborhood. Until then, I never had issues.   I do not get the same Zoom issues when connected at my office or at client sites, just on my home network.   I work from home most days, and there are no other significant bandwidth products competing with me.  The spouse is at work and the kids are in school, so there's nothing that should be taking bandwidth.  I have very few IOT items attached to my network (ring doorbell and a few cameras), so I cannot imagine they would be causing interference that would be sufficient to screw up my Zoom meetings.  Also, given the connection out and out drops for a few seconds, I likewise think it is not other things on my network.

I have had Xfinity service techs out to my house a few times in the past few weeks, and I am on my 3rd new modem.  The last tech, like all of the others, came out and did some stuff outside, then changed the connections in my wall, gave me a new coax cable, and replaced the XB8.  They then run the Xfinity tools that they carry with them, proudly showing me that my connection from the outside to the modem is always like 1.1 gig (so conceptually I am getting even better speed than I am charged for), and then do internal tests on their devices that show the speed in the 200 - 400 range for downloads.  My cellular will get in those ranges, as does the PC that I work from.  They then happily declare everything fixed and ask me to give them good scores on the Comcast survey, which I am happy to do because they do try hard. 

The next day, I do calls for work and I will experience a few issues.  The cycle then repeats.

I even opened a ticket with the level 2 advanced team, although they tell me that they are monitoring my modem and everything is fine.  Thay have no interest in looking at the results of my speed tests and latency tests that show that at different times during the day, everything is NOT fine.  They just proceed to suggest I get another technician out to do the same things again because, and I quote "we are looking at your network now, and everything is fine."  Unfortunately, there is no way I can be on the call with them precisely when I experience issues.

If I were able to segment the Xfinity network, I would do so and see if that helps.  However, the ability to do any configuration on the modem seems to have been taken away as Comcast moves to more advanced modems.  

I am at my wits' end.  

Has anyone experienced this type of issue and, more importantly, figured out how to fix it?

Thanks in advance!