OpenIGTLinkIF module is not loaded

[Sunderlandkyl (Kyle Sunderland)]

If you have built Slicer, then you will need to build all of the extensions that you need as well. The extensions downloaded from the Extension Manager won’t be compatible.

Some more info here:

Mac preview release build failed to load content in extension manager

This is the expected behavior. If you build Slicer then you also need to build all the extenions that you want to use to ensure ABI compatibility. After you have build Slicer on your computer (which is not very easy), building the extensions is trivial, just two CMake commands - see here.