50 amp circuit breaker for a 30 amp electric oven?
Actually there is a code reference for breaker sizes in this case.
The reference table is on NEC 210.24 ,,  210.21.B.2 &amp; B.3 show the tables.
A 30 amp device is a bit vague if the device draws 30 amp it could be on a 40 amp protected circuit, but not normally a 50.
In this case we would check the mfg instructions.
I have found a few cases where the mfg designed the oven for use on a 50 amp circuit.
The circuit breaker is to protect the wiring but the code also limits the maximum size breaker in article 422.11.E.3  to 150% of the devices rated current. if the oven had a true draw of 30 amps a 45 amp breaker would be the maximum size.
If the device only draws 24 amps and is rated for a 30 amp circuit a 40 amp breaker would be allowed if the device has no maximum stated.
If the device states 30 amp max OCPD that value can not be exceeded no mater how large the wire is.
So depending on the mfg requirements I would change the breaker to the recommended size because some mfg’s will do anything to get out of a warranty repair. Two large of a breaker would not cause a fault but could allow much more damage to happen and some use any reason to deny a repair.