Another Voyager owner has had a similar problem with unresponsive keys on the keyboard, although with the Old School version that doesn’t have MIDI but nonetheless, my reply to him might be the case on yours too.
I’m cutting and pasting my reply here:
“You can make sure it’s not simply the keyboard scanning circuit connections that came loose by carefully removing the Mod Wheel section and checking the connectors to that board. (Remove the two top front screws and gently lift up and pull towards you. Be careful because of the flat connector for the aftertouch is at an awkward angle and short. Reinstalling is reverse operation, but make sure the top metal panel is inserted back into its slot in the wood in the casing at the top in the back.)”