I have done a BMW E60 (CAS3+ ISTA4* version) all keys lost with Yanhua mini ACDP through OBD downgrade.
Car did not start, the customer took the car to BMW and they said CAS is dead. Can I repaire the CAS with ACDP or with different machines?
ISTA-P and short ISN is a nightmare. Always do it on bench.
Try using this special function- CAS Repair via OBD
Select the corresponding version to fix according to the version before downgrade.
If failed to reprogram the key and lost CAS file, and you have backed up original file, rewrite the eeprom and flash you saved from the original CAS and all should be fine. As long as you backed it up, you can write the data to that CAS, and if somehow that CAS was physically damaged, you can write the data to another CAS and it will work fine.
You can also send EEPROM and flash data to Yanhua technicians to manually edit the data.