I’m not entirely sure if it’s just a nuance with the autopilot I’m not understanding, or if there is some kind of conflict / msfs weirdness at play.

I'm setting my desired altitude on the S-TEC Altitude/Vertical Speed Select Programmer, and leave the VS knob at 0. I'll then engage heading mode (which I've also bound to AP ON, to mimic the lack of an actual AP on switch), and engage VS mode. All of this works and annunciates as expected with the default msfs keybinds and my hardware.

However, once I try to increase my VS via my hardware, it becomes very hit or miss. Sometimes it engages, and sometimes it does not, and I remain in level flight. Using the mouse to click the Up / Down buttons works reliably every time.