JS error on all rule select boxes

Hi, just installed this to evaluate and find that I cannot create any rules. I add a rule, then filter by product, but the UI will not let me add products. Same for many other product, category etc select fields.

Looking at browser JS console I see following error (in Chrome):

Uncaught Error: Option 'ajax' is not allowed for Select2 when attached to a <select> element.
    at String.<anonymous> (select2.js?ver=3.1:1324)
    at Function.each (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,utils,moxiejs,plupload&ver=6742d8f9006702f601b0a655d1ccbfd9:2)
  ...

I see this in Firefox console:
Error: Option 'ajax' is not allowed for Select2 when attached to a <select> element. select2.js:1324:31

I’m running WP 5.1.1 on PHP 7.x
Browsers are running on Ubuntu 18.x

• This topic was modified 5 years, 8 months ago by colinfroggatt.