Same here - also since latest 1 or 2 synapse updates (I received another update today, which did not remedy the problem).
All my synapse devices (mouse, keyb x2, mouse dock, mousemat) appear to power cycle, as if they’ve been unplugged/re-plugged into USB.
I lose control of my mouse when it happens, and it’s happening every few minutes, usually several times in quick succession before it stops happening for a few minutes. Then the cycle repeats.
EDIT: If I exit Synapse and kill all Razer Windows services, I don’t get the problem any more.
My Blackwidow V3 also disappeared from Synapse 3 yesterday. I restarted my PC and then it reappeared. I also received that update prompt, and installed it.
The day before, my new RMA replacement Basilisk V3 mouse was completely nonfunctional (not even powered on). I can usually unplug it and then plug it back into the USB port, and it will instantly be detected. This is an issue that is still plaguing those particular units. I suspect that Razer is aware of there faulty software & products by now...or they are in denial about this entire fiasco.