Hmm, I guess this is a side effect of the menu not having a sprite, so it doesn't use the sprite's animation speed... welp, it's easy to fix at least.
Set image_speed to a value lesser than 1 from the menu object's perspective (i.e. inside the block that starts with the "with(instance_create_depth(...obj_gguimenu)" call).
I find values between 0.1 and 0.2 work the best for legacy sprites that default to 60 fps, so start off with 0.15 and adjust as needed until you're happy with the result?