That is interesting.
When I get a chance in the next few days, I'll see about duplicating this in my test project and get to the bottom of why it only seems to do main hand damage. It sort of seems like now it's resetting the swing counter to zero after every hit, but then, if it were actually doing that, the weaponsprites and animations of each swing would also both be the weapon in the main hand. Either way, it's something to do with the action sequence, so I'll try to make a couple test cases and figure it out.
I'll keep you posted when I figure out what's going on, or if I need more info from your project.
Apologies for this taking as long as it is to figure out, since I stopped actively making RM games before MZ came out, I don't have a lot of experience actually using the plugins I made for it in a live project, so something like action sequences, which changed a lot between MV and MZ are proving difficult for me to get a grasp on.
-Ramza