I just tried it on a board I’d used last week and it is still working for me. I’m on a Windows 10 laptop using Google Chrome. Can you try accessing Miro a different way (e.g. different browser or via the desktop app) and see if it is happening consistently regardless of your access method?
Since it is working with Firefox, it might be some cached data issues in Chrome. I’d suggest clearing your cache and browser history and then stopping & restarting Chrome and trying again. You could also check what happens when you access the board in incognito mode.
BTW, I’m on Version 96.0.4664.45 (Official Build) (64-bit) of Chrome but not sure if that would have any relation to the issue you are experiencing.
Did a little more researching and there is more weirdness….
if I have Miro open in Firefox and I can see the add card signs. I also then open Miro on Chrome(with FireFox still on Miro), the add signs are there in the Kanban board as well.
When I exit out of Miro in FireFox, and look back at my Miro on Chrome, the add signs then disappear from the Kanban boards.