QML module not found (QtQuick Controls)

When having two or more projects opened, with different kits (example: for embedded target and for desktop target) and different Qt versions (in my case 5.12.0 and 5.9.4), QML designer cannot find modules.

How I sistematically reproduce it:

• Open a project configured for using 1 kit, target Desktop, Qt 5.12.0. Everything works fine.
• Open another project, configured for using 2 kits, one for Desktop target Qt 5.9.4, another for embedded target, same version of Qt but configured for cross compilation.
• Re-select the first project as main one.
• Clean -> qmake -> Rebuild
• After a while, Designer does not work anymore, and if I go on the "import" in the qml file, the tip text is showing all the paths, including the path of the cross compiling kit.

Attached the image of the tip.

I then need to close the projects other than the one I'm working on, and close / reopen QtCreator, let the parser do the job again, then I see again the designer working correctly, with just one project open.