"No such file or directory" error from deleted promoted widgets

[ChrisW67]

What is reporting "No such file or directory"? Cmake, moc, UI compiler, RCC, compiler, linker, at run time?
What file or directory?
It really helps to actually describe the problem.

If you manually run:

uic thingy.ui

uic thingy.ui

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and the output is correct then the problem is where the ui_*.h generated files are going or the timestamps on the files are broken and make does not rebuild them.
Delete all the ui_*.h files, rebuild and inspect the files.