If new assignments are created , the pxFlow pagegroup of the case gets modified . By only removing the assignments directly from workbasket table might cause issues with the case processing. So you might need to find all the cases which have assignment with the workbasket and Open the case and do any one of the following.
1) Process the assignment with Resume Flow.
2) Remove the assignment with OOTB utility( DeleteAssignment.- should be with px,py not sure)