We had a couple of reports of this over the weekend. As above I advised (via another moderator who picked it up first) to try a different browser and / or check that the AV hadn’t grabbed it, and both reporters have subsequently posted ads successfully. Whether this is related to my suggestion or it just worked suddenly for them, I don’t know.
We’ve spoken with Tech who have replied, “I’ve not been able to replicate it or see anything in the logs that would suggest a problem. I can only ask for people to send me as much detail as possible when it happens. Screenshots, JS console logs, etc. Anything will help”. I’d add to that, OS browser would be helpful I expect.