SLB stopped working after moving to a new hosting provider

I’ve been using Simple Lightbox with no problems for some time.
Today, I moved my site to a new hosting provider. Everything appears to be working, except that Simple Lightbox isn’t being triggered.
Things I’ve tried which haven’t worked:
* Resetting/deactivating/deleting Simple Lightbox and reinstalling/reactivating it.
* Temporarily disabling the Jetpack CDN
* Installing another lightbox, which worked–but I prefer SLB, so I deactivated it
* Temporarily disabling the All Meta Tags plugin
* Temporarily switching to the 2015 theme

It doesn’t matter if the posts were created with Gutenberg, or the classic editor.

One of the differences between the old site is the PHP version. I was running a 5.x version before, and now I’m running 7.3. (This the main reason for the hosting provider change.)

Any ideas?

I’m running WordPress 5.2.4 and the following plugins:

• Accelerated Mobile Pages
• Akismet Anti-Spam
• All Meta Tags
• Contact Form 7
• Favicon by RealFaviconGenerator
• Jetpack by WordPress.com
• MC4WP: Mailchimp for WordPress
• Really Simple SSL
• RS FeedBurner
• Search Exclude
• Simple Lightbox
• UpdraftPlus – Backup/Restore
• Wordfence Security
• WordPress Importer

I’m using The Theme Foundry’s Linen Pro theme, with a child theme.

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