Overview:
The User Activity Log shows an error: Unable to parse: ERROR: Unexpected token in group expression: Owner at index 27. What is the root cause of this issue?
Root Cause:
Offline Validation rules do not support the Owner field. The Owner Field is used to support the application global variable.
Users attempting to create Cross-Object Owner formulas to retrieve information on objects that can have owners of different object types receive this error.
Solution:
Do not use the Owner field in the validation rule.
Related Documentation:
Vault Help Documentation: Offline Validation Rules