+1, sharing the same experience.
Rebuke broke at some point during play and I wasn’t sure when/why - after reading this thread, tested removing Cast Speed and it started working again just fine.
I was getting +Cast Speed from the Sentinel Passive tree skill “Blademaster” (+Atk & Cast speed with 2H Sword/Axe) and had to unspec all points from that skill for Rebuke to function properly.
Rebuke being “broke” = “Protective Legacy” and “Solemn Vow” passives do not work - no matter how long Rebuke is channeled, if you have additional Cast Speed you will not receive the buff effect (it appears and immediately fades after releasing the channel).
Rebuke seems to still do what it is intended to do DURING the channel but after-effects are broken by Cast Speed.
If using Rebuke while moving, with the additional cast speed, the character animation also breaks and the character is locked in an idle standing pose and you can float around (kind of like a T pose, except an idle pose).