liebherr f/f

Got a liebherr f/f that needed a thermostat so replaced it wiv gen stat checked all workin fine wrote bill left etc
Next day customer phone to say not workin at all go back out find that the new stat is ko 😕 so fit an other new stat and unit works fine check that it colds down while drinkin my coffee all fine .. 2 hrs later customer phones to say unit dead not working again.. 😕 What could be causing this as both stats work for short while then both ko
Any ideas ❓