@Xykon
As mentioned by the esp-idf docs:

The OTA data partition is two flash sectors (0x2000 bytes)

Can you clarify why this is not the case for your otadata-partition?

Edit: Never Mind-> https://forum.pycom.io/topic/3161/solved-invalid-partition-table-of-otadata-size-can-corrupt-ota_0-partition/2 you are not using the esp-idf related functions to perform ota.