I found there are 2 instances of “Hidden controls issues” in the Visual Editor Tab
You may want to refer to this post (WordPress: Visual Editor Tab Controls Hidden – How to Fix?) if, this doesn’t do the trick
Basically, you go into your Post Editor (the Visual Editor) and find things are missing or hidden!
Depending on your version of Wodpress, it may be a plugin conflict.
For me, I narrowed it down to the “Simple Press” plugin
After deactivating, it returned to normal
I suggest you try the same (deactivating all your plugins) to narrow it down to the culprit