The action buttons are often all missing after opening a message. If close (back arrow) and reopen the message the buttons will appear. Cannot reproduce the problem - seems to be random, but occurs several times a day. Perhaps once about every 20 messages opened? I think it may more often happen after deleting a message, and display advances to next message which is missing buttons.
Currently running version 6.507, but has been happening for a while.
Samsung tab a10, Android 11