SKevo Hi, thanks. I think I got to the bottom of it.
Since there were problems with the email, I changed the address. Gmail didn't seem to work, used another one.
I think there is something in the flow of posting - sending notifications - getting the index updated because the error was about the sending of the notification to the user. Once that was fixed, everything started to work again.
I may open an issue about it, I don't think this is how flarum should handle an email error (in my case maximum quota was reached)
You have been very kind and helpful, thanks!