Thank you for assisting with all this, by the way. I appreciate your patience.
Alright, let’s try this now:
#1 Go to Plugins > Plugin File Editor
#2 Select the WordPress Popular Posts plugin from the dropdown at the top right of your screen.
#3 Under “Plugin Files” click on assets > js > wpp.min.js to edit this file.
#4 Replace the contents of the wpp.min.js file completely with this new version.
#5 Click on The Update File button to save changes.
#6 Set WP_DEBUG back to ‘false’.
Hopefully nothing will change and your lists will keep working but if not let me know and I’ll have a look.