Sometimes when I have written a sentence comment (intending to initiate a discussion) and try to post it, the system just answers that something went wrong, and my comment never gets posted, no matter how many times I try again.
Interestingly, it is possible to post a comment on the same sentence manually, but that’s a hassle, so I mostly just don’t bother.
Here is one discussion that I had to set up manually: Vendí mis libros barato
Update: here’s a screenshot of a comment forever lost:
