I started having the same issues with my 910 (zwave) recently.
The only observation I can add is that I left the top half cover off to see the LED lights. I noticed that when it’s paired with the hub, button 1 stays lit 100% of the time. Locked or unlocked it doesn’t matter. Even if I take the batteries out for a few hours and put it back in, button 1 LED stays lit.
If I unpair (exclude) the 910 from SmartThings that button1 no longer stays turned on.
To me, it seems like it’s constantly trying to sync or send something since one of the latest SmartThings firmware upgrades.