As per this query at mozilla, I accidentally hit some keys and a stop sign, circle with a red line through it, appeared next to y user and I then could no longer see any emails arriving from him with thunderbird.
The solution provided here to unignore the thread has not worked.
With Thunderbird 91.5.0 there is no ignore threads option in the view menu.
There are ignore thread, ignore subthread and watch subthread however in the Message menu.
I can find the hidden message with CTRL-SHIFT-F and can see under the message menu for that message that ignore thread is selected, but watch subthread is greyed out and clicking on it does nothing.
Is this a bug? If not how do you undo ignore thread?
Ignored Threadsoption should be in theThreadssubmenu of theViewmenu rather than directly in theViewmenu. Is there noThreadsitem in yourViewmenu?