[2021] Excalibur heavy finisher ability will not activate if Moon's Cut is equipped in the offhand

So I just unlocked Excalibur and could not figure out why the heavy finisher would not activate it's ability. After some testing, it seems the heavy finish ability will not activate if I have Moon's Cut equipped in the offhand. With other weapons Excalibur's ability activates just fine. Is there a fix to this? Thank you!