Recently the top menubar became corrupted while using LO.
It appears transparent - it shows desktop image, clicking on menu items (which are difficult to read) results in highlighting that follows the mouse cursor down the menu.
Menu items still work OK.
I tried deleting my ~/.config/libreoffice folder and starting again, no good.
All users on this PC are affected.
No other computer (all runing Fedora 30 and current LO version) are affected, so it was not a corrupt update as I first thought.
No configuration was altered - it just blinked in the middle of a document and became corrupted.