formcheck-yui.js:1 Uncaught ReferenceError: Class is not defined at formcheck-yui.js:1

Hi there, I've just installed CF4 on Joomla 3.9, I'm using SPPage Builder and it seems that all of a sudden the validation is not working anymore. I get this error in the title and then also the datepicker is not working. I've been trying to find out the cause, I guess it might be something related to Jquery or some script but I cannot figure it out, I've checked the forum and couldn't find a solution, I thought it might be here: http://www.chronoengine.com/faqs/2566-my-form-validation-doesnt-work.html but nope, and the link for the JQuery FAQs is not working. Any ideas what might be the trigger?
Below the full error log, any help is greatly appreciated!🙂
thanks
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Uncaught ReferenceError: Class is not defined at formcheck-yui.js:1
(anonymous) @ formcheck-yui.js:1
formcheck-max.js:1 Uncaught ReferenceError: Class is not defined at formcheck-max.js:1
Uncaught TypeError: FormCheckMax is not a constructor
at test-page.html:264
at d4a4f0293dd1207487e2829031b82053.js:19
at Array.forEach (<anonymous>)
at Function.forEach (d4a4f0293dd1207487e2829031b82053.js:17)
at Array.each (d4a4f0293dd1207487e2829031b82053.js:17)
at fireEvent (d4a4f0293dd1207487e2829031b82053.js:19)
at HTMLDocument.j (d4a4f0293dd1207487e2829031b82053.js:19)

Why are you installing CFv4 in the first place?

I need to, still haven't had the chance to upgrade my forms to CF6, they're pretty complex and it's taking months to make them from scratch

I found what was causing this issue! SP Page Bulider allows to JS compression and that was the problem, once I disabled the compression the validation began to work. Too bad though, since for JS compression is almost inevitabile to speed up joomla website😟