Omniplan Assigned value not exporting into MS Project

Good day,

I am using Omniplan on my Mac but when I export from Omniplan to MS Project - which my colleagues use, the values in the Assigned column (Task owners) does not pull through. Only blank values pull through.
Same issue happens when I open an MS Project doc from colleagues, in Omniplan - the Assigned field values do not pull through - only blank.

Any ideas on how I can resolve this frustrating issue?