Why do mapsno longer create GameMode instances?

After working in my gamemode setup for a bit, my maps no longer instantiate my game mode blueprint class.
The player controller, player state, and game state classes specified in the class, get instantiated (I can tell with the blueprint debugger, and with print statements in their construction scripts.)
However, code in the game mode doesn’t get run, including code in Event Begin Play, and code in Construction Script.

This happens even if I create a brand new subclass of GameModeBase and configure it with the same properties.
There is no error message in the logger/messages window.

This is my game mode:

I have configured this gamemode for my maps, and for my project default mode as well.
Even a brand new empty map, with this gamemode or a freshly created gamemode, does not actually run code in the gamemode.

I feel like there’s got to be something simple I’m missing, but I’ve tried setting the player controller / player state / game state classes back to defaults, I’ve tried creating a new map, I’ve tried re-creating the game mode, and still it doesn’t call code in the game mode instance, and there’s no warning/error in the console/logging window.

So what do I need to reset or clear out to make it work again?