"This comment could not be created"...?

I'm using the pdf annotation tools in box. I have a pdf that I have input quite a number of comments to, but when I select some text in teh pdf and click "Highlight and comment", when I click Post, box gives me bac an error message "This comment could not be created". And then a faint version of the comment is shown on the right-hand side of the window, together with the other comments that I have been able to create.

Two things are annoying here:

1. If I do not select any text in the pdf and just enter a comment in the text box to the lower right, there is no problem creating this comment. But of course, the whole idea with annotating pdfs is that the comment should be attached to a specific part of the pdf.

2. Every time I try to "Post" a comment that could not be created, I get a new faint version of the comment for the exact same text selection, and there is no way that I can discard those failed-to-create comments.

Is there anything I can do to be able to create new comments in the pdf? If I close the pdf and open it again, are my comments sure to be saved? How would I know?

Frankly, I regret starting to use this feature of box, it is apparently not yet ready for any serious work. Maybe I'll jus stick with the commenting function that is available in Edge instead...

Here I am using Chrome Version 93.0.4577.82 (Official Build) (64-bit)