I've just started trying to set up the for WON speed running, and just started a few runs.

I've mapped quick save/load to mouse buttons to various buttons (f/g, 7/8).

When I quick load or load after dying the game jumps straight back to the menu. I've noticed it always happens after the first map c1a0.

Does anyone know what could be causing this?

You can ask for help on discord. You may not find help here.