I've attached a minimal example with a MainWindow containing a QOpenGLWIdget. The whole MainWindow is not repainting when QSurfaceFormat::setSamples() is set higher than what machine supports.

Steps to reproduce (see Attached project):

Build a Qt Widget application with a QOpenGLWidget and set QSurfaceFormat::setSamples() e.g. to 16

Now run the binary on a second system where the graphics only allow 8 samples max.
(Reported by glGetIntegerv(GL_MAX_FRAMEBUFFER_SAMPLES, &n))

The result is, that the UI will not update correctly when e.g. a Tab is switched.
Moving another window in front of the UI will trigger the redraw of the window.

The sample settings will return the max possible
glGetIntegerv(GL_SAMPLE_BUFFERS, &n); returns 8 and not the unsupported 16
however only when setting it to 8 on compile time the issue can be resolved.

Directly comping on the second machine will not reproduce the issue, at least I could not reproduce it this way.