Hi , did you get an answer to this?
I am having the same issue , so I'm an old fashioned CE developer so not very confident in FO, but have created a new Unified Development Environment and configured Dual Write , been working through lots of articles , but I have my environment up and running and CE to FO is working fine.
I create a new contact in CE and it synced to FO fine
I am having an issue now when updating the contact in FO i am also getting this error

I'm also getting similar error when trying to release products

So both these errors do suggest a permission issue in CE somewhere
I have configured DAT and GLCO as dual write legal entities and checked
1. All four teams are configured as Sys Admin , DAT , DAT Dual Write , GLCO and GLCO Dual Write
2. F&O App Id 0000015……….. is configured as Sys Admin
3. Data Integration Service Account App Id is configued as Sys Admin
4. I even added sys admin to my parent BU default team
Any advice?