Pesky Issues Dropping Off

I’ve got dozens of Z-wave devices installed and working perfectly for almost 2 years now. Recently added a bath upstairs. Used my standard “go to” GE smart switches for the light and ventilation fan. Been wrestling with them falling off the network ever since. They will work for a few weeks at a time, then one or both will stop working entirely (EVEN MANUALLY), or they will work, but with a severe delay from the app (like 5 seconds later, will turn on/off). I’ve recently discovered if I interrupt the power to the bathroom by cutting off the breaker outside and back on (after a few seconds), it will temporarily resolve the issue until it pops back up. Any ideas ? I’ve tried boosters/etc thinking coverage but didn’t help.

Would really appreciate anyone’s thoughts here. As of yesterday, had to cut power to these again, but immediately started working, responding again - physically and via the app - as expected. Any ideas why a power-cycle at the panel would magically make these GE switches start working again ? Wondering if a month is just a coincidence (from my original post).

Bumping after edit. Thx for any help !