I just tried to enable WYSIWYG editor in textbox field but run to issues with it. When trying to load the form it does not complete loading and I can see several errors from console:

Uncaught SyntaxError: unterminated regular expression literal 458d7ae7b1abbd7f0769f210bc333798.js:8:1589
Uncaught ReferenceError: tinyMCE is not defined
<anonymous> xxx.net/xxx/index.php?option=com_jce&tas...4c664fe3810c19362d:1
index.php:1:1
Uncaught ReferenceError: RSFormPro is not defined
<anonymous> xxx.net/xxx/index.php/en/en-club/en-club-posting:63
en-club-posting:63:10
Uncaught ReferenceError: RSFormPro is not defined
<anonymous> xxx.net/xxx/index.php/en/en-club/en-club-posting:70
Uncaught ReferenceError: RSFormPro is not defined
<anonymous> xxx.net/xxx/index.php/en/en-club/en-club-posting:72
en-club-posting:72:10
ReferenceError: WfEditor is not defined
<anonymous> xxx.net/xxx/index.php/en/en-club/en-club-posting:73
en-club-posting:73:2374
Uncaught ReferenceError: RSFormPro is not defined
<anonymous> xxx.net/xxx/index.php/en/en-club/en-club-posting:74
en-club-posting:74:10
Uncaught ReferenceError: RSFormProUtils is not defined
<anonymous> xxx.net/xxx/index.php/en/en-club/en-club-posting:75
en-club-posting:75:10
Uncaught ReferenceError: ajaxExtraValidationScript is not defined
<anonymous> xxx.net/xx/index.php/en/en-club/en-club-posting:78

My first guess was that the issue is with JCE Editor. I enabled Front End profile separately for JCE Editor, set it first in order of profiles and made sure that it has "All Components" selected plus also assigned the profile for the user group. However, when I switched default editor to Tiny MCE the issue and error messages where the same.

Any ideas how to fix this?

Seems like an issue with an extension compressing the Javascript on the page and creating syntax errors.