I don't fully understand the problem yet, but it seems to behave like the following.

I have:

• at least two Creator instances open
• manually add a new Qt version, Compilers and Debugger (after offline installation on Windows)
• create a new Kit of them
• save the settings
• build a project with this Kit
• close this Creator
• close the other Creator instance afterwards

When opening Creator again, the Kit and all manually set-up Compiler and Debugger are lost.