Plugin Dev Help Debugging White Screen (Editor Fails to Load) / Blank Posts List

I have been adding Gutenberg extensions to a couple of related plugins, RSVPMaker and RSVPMaker for Toastmasters, and am seeing the benefits. However, I am currently wrestling with an intermittent bug that occurs only in a few circumstances but is proving very difficult to debug. I have seen some other posts about “white screen” problems, and I’m hoping someone who reads this will have seen something similar and will clue me in on what to look for.

The most puzzling thing is that on a multisite install, the error occurs on some subdomains but not others — with no obvious configuration differences between them. To my great frustration, it works perfectly on a subdomain used for demo purposes but not on the subdomain I’m using in production.

In these cases:

* The editor fails to load post content (a white screen is displayed with no controls or content). No errors are displayed in the JavaScript console.
* The post listing screen also comes up blank. The table listing the posts sometimes appears for a moment and then vanishes. I haven’t been able to find any CSS or JavaScript code that might be setting display: none. In this case, I have seen some errors on the JavaScript console but I have been unable to trace them to any issues with my code (error log listed below).
* The issue seems to be related to blocks I have defined for use with the RSVPMaker for Toastmasters plugin, used to define meeting agenda items. If one of these blocks is included in a post (for my event listing post type), the post will not display properly in the editor and the listing of event posts will also fail to display — but, again, I’m only seeing this in certain subdomains of a multisite install. In other circumstances, it works fine.
* I am puzzled by why the content of a post would cause problems on the post listings page (if that’s what is going on) since it is a listing of titles and metadata, not post content.

Screenshots and code shared on Github

The page I need help with: [log in to see the link]