Got an answer from PTC tech support. Ends up it was an error in my code!
Previously, I had been defining my action as:
err = ProCmdActionAdd("LM_refit",(uiCmdCmdActFn)LM_refit, uiProe2ndImmediate,(uiCmdAccessFn)ACCESS_AVAILABLE,PRO_B_TRUE, PRO_B_TRUE, &cmd_id);
The problem with this was that ACCESS_AVAILABLE needed to be the RESULT of the uiCmdAccessFn (aka, a function that responds with what the proper access should be). So the proper result would be something like:
Err = ProCmdActionAdd("LM_refit", (uiCmdCmdActFn) LM_refit,(uiCmdPriority) uiProe2ndImmediate, (uiCmdAccessFn) ToolkitMenuAccess, PRO_B_TRUE, PRO_B_TRUE, &cmd_id);
------------------- where there exists a separate function ------------------------------------------------
uiCmdAccessState ToolkitMenuAccess(uiCmdAccessMode access_mode)
{
return ACCESS_AVAILABLE;
}
So ultimately, where I thought my code wasn't debugging properly because of an improper setup, it really WAS set up properly the whole time, and I simply had an error in my code that was going unnoticed... so I'm going to call it a "beginner's mistake" 
haha.
Thanks for everyone's help!!