Putting the +1 before the zero-extend will allow scalar evolution to fold the expression in some cases.
This issue is first tried in https://reviews.llvm.org/D91724 and seems there is some issue with that patch. This patch fixes the issues in that patch.
You're using a variable called TripCount to store an ExitCount (e.g. BTC) before adding the appropriate offset. I strongly suggest using two variables.