Mass Transfer Approval requests throws Insufficient Privileges error

If users are encountering the following error:

"Insufficient Privileges — You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary."

Please verify whether the related Process Instance/ Process Instance Work Items are currently in a Pending status. When an approval request is pending, the associated record is automatically locked to prevent users from making changes while it is going through the approval process.

In this scenario, the ability to edit or transfer the locked record depends on the Record Editability setting configured for the classic approval process.

If Record Editability is set to Administrator Only or an Assigned Approver in the approval process configuration settings, the user who is performing the mass transfer should meet below criteria:

1) User should meet the Record Editability criteria for all the approval request records.
OR
2) User must have the Modify All permission on the related object in order to transfer the record or make changes to it while it is locked.

For more information about Record Editability in approval processes, please refer to the following article:

Specify Who Can Edit Locked Records in a Classic Approval Process