Sorry, I posted an incomplete project, I made quite some tests and posted the wrong one.
Further tests show that the problem happens when using the class file in the project instead of the b4xlib.
Attached the 'new' project.
Then, removing the xRotaryKnob module, and using the xRotaryKnob.b4xlib the problem persists.
And then, commenting these two lines in Designer Script it works again.
'xRotaryKnob1.Left = 10
'xRotaryKnob1.Top = 50