When I opens Thunderbird, I sometimes have a problem with the sending/receiving screen (once a few days). The problem is that the upper part of the screen disappear. I can not perform some of the operation on the screen because some of the icons on the upper part of the screen disappears. When the above problem occurs, I have the same problem with the explore screen of Windows 10 (the upper part of the explore screen disappears, which also causes a problem to me).

I am not sure this problem is a matter of Thunderbird or Windows 10. 

This problem has occurred for around two weeks. I can not find any specific reason for the problem. To solve the problem, I reinstalled the latest Thunderbird (ver. 78.3.2 (32 bit)), but the problem still exists. The screen recovers after PC is shut down and started again, but the problem occurs again after a while. I can not find when the problem occurs. It seems to me that the problem occurs suddenly. Please give me a suggestion for the solution. PS I can further send the screen with the problem as a attached document to someone who sends me a helping e-mail (for easy understanding what the problem is). Naoki Tsukamura