Ok so it's 5AM and i spent the entire night on this shit 😅 The last Wordpress update broke our newsletter subscription form in the widgets. There was a jquery error in the console so I tried moving the jquery scripts to the footer but nope... Looks like a caching issue so I disabled Cloudflare and Pagespeed but nope.
Finally found the problem. It's the stupid Mailpoet plugin we are using. This thing is crap it looks like abandonware and they want to push their new version. We will have to find an alternative soon. Anyway, the problem is that the plugin uses an old version of jquery.validationEngine.js calling a size function that is not available in the most recent jQuery versions. So probably the wp updates also updated the version of jquery.
I downloaded the most recent version of jquery.validationEngine.js on github, then uploaded it to overwrite the file here:
I'm writing this because it's possible that a future update of wysija-newsletters will overwrite the file again, so we just need to do the same fix again
p.s. ditch this crap asap