Trying an unsheilded HSI seems like a cheap experiment to try.
I'd be going for an un sheilded 120V HSI that can be FIRMLY locked into your HSI bracket. Most have a groove in their base to match the brkt to secure their position. Your main concern is that the HSI carbide can not move to contact any metal or it will short out. It obviously needs to be in the burner flame path but shouldn't be so obstructive as to divert the flame path from the exchanger opening.
Either it will work seamlessly (problem solved) or your problem is something else and you can always put the old HSI back .