Plugin breaks with basic use

I've added your plugin to a client's website, and they've reported a bug where using Suggestion Mode causes the page to crash. I just recreated the bug myself. It's happening to users with the Editor user role, but apparently not to Admins. To replicate the bug, I created a new post as an Editor and saved it as a draft with a simple text block. I then turned on Suggestion Mode and began making suggested edits, and after making a few edits I got a popup saying "That's an unexpected error! Sorry about that!" After the popup appears, any unsaved work on the post is lost. I've attached a screenshot below. Do you have any idea what might be causing the error? The plugin mostly seems to be working, but these errors crop up sporadically without any clear trigger besides working in Suggestion Mode.