I just added two Sensative Strips Guard 800 to my network on C-7. One I included manually, and one I included using SmartStart. In either case, after inclusion, I had to change the device type from “Device” to “Generic Z-Wave Contact Sensor”. The one I included the old fashioned (non-SmartStart) way reported battery level once. The other that I included via SmartStart did not. And no matter how many times I move the magnet to the end of the strip and pull it away again, neither will report an open/closed event.
As far as I can tell, nothing shows up in the log, either.
I would suggest the Generic Z-Wave Plus Contact Sensor driver, but I don't think that will affect your problem. Is it possible they lost Z-Wave communication with your hub, perhaps due to range or other problems? (This seems less likely for the one you included using SmartStart, which probably put the device in LR mode, though you can check Z-Wave Details to see for sure--though it could still take it a few tries to adjust power if you moved it.) Are other Z-Wave devices working OK? Do you have any "ghosts" or other possible problems on your Z-Wave network? See: How to Troubleshoot Z-Wave | Hubitat Documentation
For Logs, one thing you'll also want to do is enable debug logging, then see if anything happens on open/close. If you don't see anything in Logs at all, that's a good clue that nothing is coming in from the device, pointing to one of the above problems. If there is some sort of report, it's possible the driver just isn't parsing it correctly (into an event you'll actually see elsewhere).
I'm also not sure anyone has tested the 800-series version of these devices, though I can't imagine they're that much different from the (supported) 700-series devices or really any other Z-Wave device...
Actually, this seems to have fixed my problem. Go figure.
The missing logs were because I changed the device names after adding them. When you click on the Logs button at the top of the device page, it takes you to past logs for the initial default “Device” name which, naturally, doesn’t pick up anything with the new device name. I can see them in live logs, however. That seems like an unintended feature in the hubitat UI (I’m still on 2.3.8.140 - unsure if this is fixed in a newer version).