[REG 4.8.2=>4.9.0] Code completion in cmake project not working on Windows

I cannot provide the whole project (it is big and not open source), but on Windows the code completion completely fails in a larger cmake project.

Nothing happens in any of the files even in basic classes. It also does not work if the code is plainly written in the top of a file.

The code completes on Mac and it works with earlier versions of Qt Creator. It may be a settings issue, but removing the QtCreator ini-file didn't help. (I have not tried to remove settings on Mac).

Is there anything I can do to assist in finding out what goes wrong?