After upgrading to version 15.6, the New UX displays the error when adding a resource as the Owner of a Task:
API-1011: The given offset 'XXXX' is invalid. Must be a whole positive number and less than total number of records.
consistently reproduced or is it intermittent?
The search results will also not display.
The user browser cache is outdated.
Proceed to clear the user browser cache.
Please reference article:
This was reported as DE43615 and is fixed in 15.5.1 and 22.214.171.124 (Patch 1)