It would be better to contact ESRI Support to better handle this issue. They may require more information regarding the issue to better understand it like,
1. Is it version or user or client specific issue?
2. Do you face this error if you edit the same layer using same user and version from Desktop 10.3?
3. Did you also upgrade the geodatabase during system migration from 10.3 to 10.4?
4. If geodatabase was upgraded, what were the steps followed? Were any issues encountered?
5. Version of Oracle being used, type of connection etc.
Thank you!