Overlay but no post pop-up

[Gah!! I added a whole bunch of useful stuff in a reply to this similar post, but a forum moderator just sent me an email asking me to submit a new post and deleted it all. Including my post in the body of the email would have been helpful, guys. Hopefully I’ll remember enough.]

The issue: clicking on an item in the calendar brings up a dark grey modal overlay, but no post. This happens in Grid and List view in the front end (List view is OK), and Grid view in the admin screens. I tried the Settings > Display tweak suggested in the pinned post. Still had the issue.

I was using My Calendar 3.8.3 on WordPress 7.1, GeneratePress theme.
I also tried switching to Twenty Twenty Five and deactivating all other plugins. Still had the issue.

I’ve rolled back to 3.7.17 for now, but ChatGPT suggested some tests…

ON CLICKING IN FRONT END
No change to html or css

ERROR IN CONSOLE
Uncaught TypeError: Cannot read properties of null (reading 'getAttribute')
at P.insertAdjacentElement.modalText (accessible-modal-window-aria.min.js?ver=3.8.3:1:3985)
at HTMLBodyElement. (accessible-modal-window-aria.min.js?ver=3.8.3:1:4608)
P.insertAdjacentElement.modalText @ accessible-modal-window-aria.min.js?ver=3.8.3:1
(anonymous) @ accessible-modal-window-aria.min.js?ver=3.8.3:1

TESTS IN CONSOLE
document.querySelectorAll('#mc-modal-page').length
1
document.querySelectorAll('[data-modal-content-id]').length
53
document.querySelectorAll('[aria-haspopup="dialog"]').length
53
document.querySelectorAll('dialog').length
1
document.querySelectorAll('[role="dialog"]').length
5

Likewise… ADMIN SCREENS ERROR
Uncaught TypeError: can't access property "getAttribute", x.querySelector(…) is null
j https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
j https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
j https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
j https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
t https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
EventListener.handleEvent* https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
https://hukeleymissioncommunity.org/wp-content/plugins/my-calendar/js/modal/accessible-modal-window-aria.min.js?ver=3.8.3:1
accessible-modal-window-aria.min.js:1:3959

Thanks Joe,
No Through Road

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