Firefox 55.0.3 on Windows 10.
If you enter a comment in a task and click the center of the blue button (where the “Comment” text is), the submit fails and the comment field scrolls down. It took me forever to realize that that’s because the Comment text itself is interfering with the submittal! You actually need to click on the padding outside the text for the submit to go through. Not sure if this affects other browsers as well.