This happens when the Date Time Modified (DTM) stamps on the files in the module get set to 0.
I have this happen to me every now and then and I have never been able to put my finger on what causes it.
The only solution I have been able to find (on Win 10) is to extract all the files from the module, use a 3rd party tool to set the DTM to something (e.g. today) and then zip the module back up. It should do one more tile the next time you open it, then be fixed.