Adding comments to certain commits does not work - field does not respond to entry

Certain recent commits to my repository do not work when I try to comment on them, but others do. I have tried multiple users, multiple computers, multiple operating systems, and multiple browsers, all with the same result.

In the commits that don't work, the field is there to type in a comment, but when typing something into it it doesn't react. On other commits, the field expands as I typed stuff in to give more space and show editing buttons, but now it stays as only big enough to show one line at a time.

More importantly, the button to actually submit the comment never appears, rendering the field completely useless on these commits.

See comments below for more details and examples.