I have encountered the "conditional mandatory fields are hidden but cause validation error" problem. Its happening during the registration process in the following 2 scenarios:

1) A tab, which has some conditional mandatory hidden fields, is itself initially hidden. The tab is shown later on during the registration process based on cb tabs conditional. Validation errors are given for this tab after it is shown and when you try to complete registration. I have prevented this tab from being initially hidden to test this problem and i get no validation errors from the mandatory hidden fields.

2) Fields that are hidden based on the subscription plan are giving validation errors. So far only affected fields for this appear to be editor text area fields.

Any help with this would be great. Let me know if you need more information.

Joomla! Version 3.6.2 Stable [ Noether ] 4-August-2016 23:41 GMT
PHP Version 5.6.24
mysql version 5.6.32-78.1
community builder version 2.0.15+build.2016.09.18.15.00.02.b2e3df5e1

No they are both two different scenarios and two different sets of fields:

The first scenario is with cb conditional only where tabs and fields are conditionally hidden.

The second scenario is with cb subs on a tab that is always shown.

The tabs and fields in the first scenario are different to those in the second scenario.

cb subs version: 4.1.0+build.2016.09.02.14.13.49.ae734b9bc
cb conditional: 4.0.7+build.2016.07.09.00.28.00.ec65dbf5d
cb version: 2.0.15+build.2016.09.18.15.00.02.b2e3df5e1

Only the second scenario with CBSubs is throwing validation errors or are both them throwing validation errors?

They are both throwing validation errors and both scenarios happen independently of each other.

The top of the page should state what fields failed exactly.

It doesnt. Only the tab text appears red with the red X next to it

In the case of CB Conditional this can happen if you've conditioned a field more than once or you're using a condition it can't complete during PHP processing.

The cb conditional field scenario does not throw validation errors when the tab the fields are on is not initially hidden so i dont think this is the case. The validation error only appears when the tab was initially hidden.

i have attached a screenshot of the html showing the hidden fields with validation errors if this helps at all.