Login form of resellers brand remains CCP v1 style even though CCP v2 is enabled.
If provider has CCP v1 enabled by default, the login form style is inherited for child resellers. That unexpected behavior is caused by software issue #APS-42838.
The fix is planned to be included in one of the future product updates. Contact your Technical Account Manager or PTA team (firstname.lastname@example.org) to trace the status of #APS-42838.