OK, here's an old mechanics trick : get a spare H7 headlight bulb and wire it across the fuse socket.
That way when the light gets real bright, you know you are in the "blow the fuse" condition.
( if you connect it with long enough wires, you can even have it on the cowl with the hood shut so you can drive )
Maybe you can determine what's happening at that time.....

Caveat : the light will not "blow", so there is potential for damage using this method, try at your own risk !