I ran into two problems with the 'IK separated Trans and Rot ctl' build in the epic arm component. Noticed the problems in 4.30, and they're still around in 5.0.6

matching FK to IK when using ikRot values doesn't correctly match. It looks like the fk2 match ref is always built on the IK controller, even when building a split rig. Switching the ref target during the build seems to fix this
around line 440

        if self.settings["ikTR"]:
            fk_ref = self.ikRot_ctl
        else:
            fk_ref = self.ik_ctl

        self.match_fk2 = self.add_match_ref(
            self.fk_ctl[2], fk_ref, "fk2_mth"
        )

Second, when matching on a rig built using a custom naming convention the match errors out and doesn't switch trying to find ikRot_mth, it appears to be because that mth node is created using addTransform, instead of add_match_ref
around line 715
self.match_ikRot = self.add_match_ref(self.ikRot_ctl, self.fk2_ctl, "ikRot_mth")

I didn't check if the same fixes would apply to the other arm components, but it seems likely.