When user select multiple tasks with various statuses (Ready, Reserved) including the ones being in states not allowing reassignment (Suspended, Completed), then the bulk reassign operation fails.

That's different behavior from the others bulk operations.

When user confirms the reassignment dialog, an error popup appears:

When the message disappears the dialog stays displayed, and can be closed by the 'x' button.

It seems that the tasks that are in correct status are being processed correctly even though the UI behaves unexpectedly. It is just disturbing for the user.
The fact whether other tasks are being processed depends on the order of tasks, no task is processed after one of them fails.