id you also nuke the build folder ? Did you move your project in a different path ? Did you rename the path/folder containing it ?
I've done the first. Then I just copied my project folder from my pc and opened project on usb drive - it worked. But starting from scratch (deleting every qt-creator related file, like .user) didn't help. So i just moved directory completely and it worked. It's still very strange because Git didn't any changes in project files so only hidden by gitignore remains and I'm pretty sure I tried to delete them.