Oven 40 amp breaker tripped, replaced with like kind, no 240 volts
Because your panel is a GE Qline

The original breakers was their 1" wide 2-pole breaker. The type straddles two spaces, leaving 1/2" above and below.

You took it to the store, I am guessing a big box, and looked for breakers like that.  They didn't have GE 1"  2-poles. But you or they mistook it for a duplex.  

GE does not make duplex breakers.

But you found a BR, HOM or Murray duplex. Close enough. The clerk swore it would fit. He "knows" all these types cross-fit  (wrong). 

You got it home. It wouldn't fit directly, because it couldn't clip on to those little Qline cruciforms on the bus bars.but did fit if you moved it to a different location.

Moral of the story is don't use alien breakers.