Mail app - combined inbox no longer working

In Mail the 'All Inboxes' no longer shows received emails, I have to look at each individual inbox for all 6 of my email accounts. All my accounts are showing in the 'All Inboxes' section and, for some reason, the inbound emails have just stopped appearing in the combined inbox. Not sure what I have done but the latest Mac update seems to have made this change and I can't see what has changed, or needs amending. Any help would be appreciated. I am not having this issue on my iPhone or iPad, just on my Mac Studio and MacBook. When I hover over the plus sign to the right of the favourites header the pop up shows 'All Inboxes' as ticked and is greyed out. Any help appreciated