Orbi RBR752 unstable internet, notifications come in batches

I have an Orbi mesh at home (AX4200) with the router and one satellite. I use the Netgear CM1200 cable modem. I'm on the Xfinity 1.2gbps plan, but the CM1200 limits me to 1gbps. The speed test on the Orbi app generally hits 941 Mbps down, 42Mbps up. This has been working well enough since April 2021...until the last couple weeks. I can get up to 700Mbps on my Galaxy Note 20 Ultra 5G, and reasonable 300Mbps +/- on my laptop's wireless connection. I'm good with all of this. However, over the last couple of weeks, the notifications on my Note 20 come in batches. I'll use the GMAIL app, for example, with zero notifications showing. The app loads, I have new mail, and suddenly the Note lights up with new email, maybe ESPN Fantasy Football alerts, LinkedIn alerts, etc. So I basically have to access any app that is enabled with notifications and then all my notifications come in. The same Note 20 gets the alerts in a timely manner when I'm not connected to the Orbi.

Note that I've rebooted the CM1200, then the router, then the satellite multiple times. Since this problem started, I regularly get "your internet connection is unstable" messages in Zoom (laptop). When I review the logs, I'm reminded how inadequate they are. I run a speed test when I get those errors, the throughput is fine. So it's hard to properly define the problem aside from notifications from multiple unrelated mobile apps come in batches and wifi connections are randomly unstable.

I'm dead stumped. Apparently the support for these is very time-limited. I'm six months in on this solution, and no support. Any ideas? I'm ready to dump this system.