Forms creator has disappeared

[Proctobot]

I'm running WP 5.9.3, for which, for some reason Event Organiser Pro 3.3.6 has not been tested even though this is not even the current WP version. Updating from a much earlier version (necessary due to changes in Stripe verification) has resulted in the form editor completely disappearing. Is there a fix for this, or should I abandon this plug-in? Why isn't Event Organiser Pro keeping up? Here's the md file:
event-organiser-system-info-NHIG.md

[stephenharris]

Hi, the 'tested up to version' doesn't automatically get updated, and I've neglected to update it in recent updates. The plug-in should work with 5.9.x (and 6.0.x for that matter).

One thing I suggest doing is checking the browser console. for errors on that page. If the form builder is not appearing that it's almost certainly a javascript related error, and the error message and source file might help indicate the cause.

[Proctobot]

There are 73 lines of Javascript error code in the console. I don't know where to begin! Is there a fundamental problem here causing this? Perhaps the theme? The theme is Organic Non Profit, and it's very old.

[Proctobot]

When clicking on the ‘Booking Form’ tab within the admin settings of Event Organiser Pro, the page remains blank.

/wp-admin/options-general.php?page=event-settings&tab=booking-form

Within the browser console we have the following error message, which is looking for an unset varible array named ‘locale’. This is requested by one of the plugin javascripts (booking-form.js:2:138)

uncaught TypeError: this.locale is undefined
gettext (then the pathto booking-form.min.js?ver=3.36:2)
anonymous (same path)
anonymous (same path)
gettext (same path)
anonymous (same path)

This variable hasn’t been set; is it something which would normally be set by Wordpress? I have checked the wordpress settings, the language and location has been set / altered to test if this makes a difference (without luck).

While this error is happening within the admin (admin is not themed, so it is unlikely to be a problem with the theme), the form also does not submit on the front end.

If you could take a look and point me in the right direction, or give me an example of what this variable to should be so that I can set it manually, that would be most helpful.