This issue is slightly different than the root cause in the KB identified by Liz.
For this specific case, after further investigation, we found that this issue is caused by a change in the data type from a LARGE STRING to a STRING.
Deleting the Large String attribute and creating a new attribute as a String type reusing the same attribute ID
We logged a bug : CLRT-79097 and found a possible workaround by deleting the new attribute (created the 2nd time) and then recreating the same attribute again a 3rd time with the data type of String ... . thereby causing the application not to think there is a change in the data types.
Reference
Portfolio Sync failed - Can't use Portfolios
Document ID: TEC1348932