I'm finding that when selecting some messages, once opened the screen flashes on and off. Sometimes it settles down but otherwise it continues to flash. In addition, when there is more than one page of posts, the following pages content are not always displayed. Indeed, when selecting to preview this post all I get is a flashing screen!
After several days with the issue the problem seems to have resolved itself. I'm guessing, from the lack of comments from others, it was just me with the problem. Perhaps my computer was just tired of over use during lock down
As a possibilty to consider, if you are using a laptop, a common fault is the cable that joins the chassis to the screen (and hence flexes everytime you open the lid) can develop a fatigue fault that does sometime lead to the symptoms you describe...