Are you able to see if from the customization preview? If there are multiple customizations for the screen I have seen some get stuck. It took me deleting the unique customization, ensuring the user could see the ALL/ALL customizations as expected, then I was able to recreate the screen for that specific user.
The strange part, was that I could see the customized panel from the Custom Office > customizer task, but NOT from the right clicking on the screen customizer.