"An Unidentified Error Has Occurred" – Taxonomy Errors

After adding new taxonomies to my custom post types, all seemed to be going well, until I tried adding items to those newly created taxonomies.

After filling in the information and clicking “Add New X”, nothing happens. The page doesn’t move at all.

However, the taxonomy is still created; if I refresh the page manually, the taxonomy is there, but the text boxes I just filled out for it are not cleared out (they still show the contents).

I created a dummy item to test this under one of my taxonomies, and when I tried to delete it, I got the message at the top “An unidentified error has occurred”. However, after refreshing the page, the item was indeed properly deleted.

Any suggestions?

https://www.ads-software.com/plugins/custom-post-type-widgets/