Missing .dylib

Following along with the Twin Stick tutorial series on YouTube and have hit a roadblock. Closed my project and when trying to reopen, am seeing this. Have tried changing UE versions and still not having any luck. Any ideas?

The following modules are missing or
built with a different engine version:

UE4Editor-TwinTutorial.dylib

Would you like to rebuild them now?

FWIW, I started a new project and manually moved all content over (via Finder) and that seems to have remedied the issue. Would still like to know what triggered the issue. Using UE 4.12.2.

I also see this after making a clean build, I think, the UBT has problems when switching between Development and DebugGame. It also loads wrong dylibs (old versions).