Stylesheet call fails

I activated the theme on a new site and all was well until I used the customize page. Within 5 minutes style.css was no longer getting called. Deleted it and reinstalled and the same thing happened again. Updated from WP 4.4.3 to the latest version, no change. Switched to other installed themes and there was no issue with them.
So without doubt, there’s something fundamental wrong with this theme and I can’t recommend it when there are so many other themes that work fine.