I published a new flatly zip file onto the appstore. Hopefully this solves your issue. Looking at the code on GitHub. It looks like i had updated the themes to support cachebust. I must have missed this one when i updated the files.
If you want to view more information on these themes then this repo is helpful:
If you re-download the flatly theme. It should work correctly. If not raise an issue on the Github repo.
after doing all those changes did you clean deployment directory before rerunning the project? its under project > clean deployment directory. If you added the cachebust parameter to the index file that should fix the issue.
These themes were created in an older version of Mendix and hence why they don't work. If there is enough demand for these themes i'll update them to the latest version of Mendix. As i created the original versions.
Who else would like to see these themes updated? If we get enough people i'll spend some time to get them upgraded.
Since you mentioned replacing the index.html file in your theme, I assume there's no other ZIP file of your theme in that directory?
If that's not the case, make sure the Project settings point to the correct files. Check to see whether Theme (under tab Runtime) is set to the zip file or (Default).