Just to confirm I am also getting the same problem at https://forums.windowscentral.com, however there doesn't seem to be a thread there on this topic. thanks.
I'm trying to create a new post in the pixel forum. Initially I tried text with 3 picture attachments, and got the error. So I thought maybe removing the attachments would fix the problem, but it still occurs when I just post text. I also tried using a different browser as well.