Drunk and fishing in the dark 
Did you extend the top beam to 5 M?
Left Chain Length Greater than System Settings Chain Length LeftChainLength: 5415.68 System Chain Length: 3810
You did not extend your top beam to 12ft and increased the length of the chains without telling GC that?
Feel free to ignore all comment till 8 hours in the future 
Edit: Sorry, was meant as a joke. Looking at it now, it was a bad one.
Wouldn’t a broken gear with the encoder intact give exactly this feedback?
Edit2: A slipping sprocket would do the same, if the screw is not tight on the flat side of the motor shaft.