OpenGL and HMI refresh

Hi there,
Working with Juce 6.1.6 and OpenGL, I struggle with something “quite” simple:
I cannot update any components while in my lambda passed to the executeOnGLThread() function of the OpenGLContext. Apparently the MM is locked and so no progress dialog can be shown.
Am I missing a point here?
Thanks if you can guide me on this…

Finally I managed creating and deleting the progress window outside the executeOnGLThread() call.
But the repaint of the progress bar is weird: sometimes it is, sometimes not.
Have you an hint to force it to be repainted while in the executeOnGLThread() please?