Bug/Issue Error in Many a Mage

I'm having a problem playing co-op Double Trouble online with a friend. Both of us are on Steam, and it doesn't appear to affect their game. This problem has happened twice to me though, both on the same level: "Many a Mage," the second in the Cherrystone segment.

In both cases, it was my co-op partner's turn, they move a unit or make an attack, and then my game stops. The first time it happened, it crashed on turn 8 with this popup: "Halley has aborted with an unhandled exception: invalid vector<T> subscript." In a completely new campaign with a different partner, it booted me on turn 6 to the main menu with the error message "An invalid unit order has been received." Trying to rejoin either of these games repeats the error, rendering them unplayable.

Both lobbies are still open and the lobby codes are in the title of the crash logs, if that helps.

Steps taken already:
- Steam and computer restarted
- Video drivers updated w/ clean installation
- Visual C++ repaired
- Game files verified, uninstalled & reinstalled
- Antiviruses disabled
- Other keypads/controllers unplugged
- Game put into OpenGL mode
- "-skip-intro" added to launch config

I really enjoy this game and the things you've added in this DLC, so I hope to get back into my campaigns if possible. Thank you for your help.