When editing a custom field group, Toolset does not allow duplicate field labels. This is fine and probably desired most of the time, but one exception is having an identically labeled fields in separate repeating field groups. This should be allowed, but currently, Toolset prevents it as an error.
Example:
Repeating Field Group #1
Label: Email
Slug: group-1-email
Repeating Field Group #2
Label: Email
Slug: group-2-email
This is perfectly valid, but Toolset will refuse to save because the labels are the same. The problem stems from the jQuery filter at /vendor/toolset/types/resources/js/fields-form.js:759
$('.wpcf-forms-field-name')
This filters out duplicate field labels EVEN ACROSS repeatable groups.
I believe the correct solution is to run the check once for all fields outside of a repeating group, and then run the check again for each repeating field group.