Last night I switched out the Gateway router for another unit. We'll see if the problem persists. If so, it would go a long way to confirming your theory that it's a non-local issue.
Good luck! I had an extended support session with Verizon — they pushed some changes to the route (god knows what) and then I rebooted it again after the session was over. I ran a Wifi sniffer to see if there was channel contention with the networks around me (I live in a residential area and don’t have to deal with bad density) and found a couple of other networks running on the same channels. After dealing with that, I rebooted it again and thus far, Zoom performance has been improved. Will keep monitoring it and post here if anything changes.