The studded rectifier is suppose to be anode to case.
The ones I use have the part # NTE 5991 on them and rated at 40 amp / 400 volt and when those are used up I will be switching over to the 40 amp / 600 volt 1N1190AR from All Electronics which others on the forum have recommended because of the higher voltage range.
I have been installing these for years and never had a problem as you are describing.
The only thing I can think of is you have the wrong one.