Apple watch ultra 2.0 stoped working….apple support not supporting

my Apple Watch Ultra 2.0 stops working suddenly. It is happening for last one month. It suddenly stops working whenever battery touches 50%. I took it to store 2 times in a span of 20 days and every time they update software and return to me. I can see panic error in the diagnostic log. Which means there is serious issue in hardware which they are not believing and taking action. My watch is covers with apple care +. But still they are not replacing it. What should I do?