I tracked mine down to a bad Schlage Connect lock.
A little background - I bought two Schlage Connects a year or so ago, and one of them would drain the battery pack in a month while the other was still on the first set of batteries after a year.
I called Schlage, and they had me give them the firmware number on the lock that awas draining batteries, and told me it was a known issue with that firmware so they would send me a new lock free of charge. They said I didn’t have to return the malfunctioning lock, just keep it for parts.
Long story short, I installed that lock on the back door in our kitchen since I had it laying around and that door isn’t used much, so no big deal if the battery drains since it wouldn’t be doing much motorized operations anyway.
Once I took that lock out the lock manager version 6.0.1 worked fine. There were a couple of avenues I tried to confirm it was indeed that lock, so there’s a number of techniques you could try to get the lock manager working again:
Downgrade the lock manager smartapp to a previous version (this worked for me since I kept a copy of the old code) and then remove the lock having a problem, then upgrade the smartapp.
Or you can delete the smartapp from the IDE, add it back (with 6.0.1 code), publish and install, and then add one lock at a time. For me, when I added the bad lock to the SmartApp it jumped to an error screen and wouldn’t save. It would allow me to go back and remove the problem lock. Once I narrowed down what lock was causing the problem I added all the other locks and it was fine. So I ordered a new lock to replace the old one.
Exclude the bad lock (if you know which one it is), acknowledge the warnings that it will affect various smartapps and routines depending on your setup, and the lock manager app will work.
So at least in my case it appears that a bad lock was causing my issues. Everything is working here and I have a new lock on the way. Hope this makes sense, let me know if any question I can help answer.