Hi Daryl,
Thank you for the proper details, it helped a lot!
I have found the cause of the issue, and fixed it as well. This option had to be changed to the default value: https://i.imgur.com/5LhJmQy.png
I’m guessing, that there might be a shortcode/filter registered by that plugin which may not work in ajax requests, or out of post context.
Now it should be working correctly as before.