Hi, thank you for your replay, sorry for pushing, have this error on the live server and need to solve it asap.
I have contacted wpengine support they said its plugin issue and need to update it. I will contact them again
Answer for your questions.
1. Yes, it was working fine and just stopped to work when I added the new field.
2. There is no other areas with this error
3. I didn’t try that, fill free to do that on staging server
4. I didn’t try to swap to default theme