No file content sent. - error shown on bulk smush dashboard

First, the plugin seems to rarely be able to smush more than 1k images until is just poops out and stops - but this maybe normal.

The issue now is I get this output: No file content sent.No file content sent.No file content sent.No file content sent.No file content sent.No file content sent.No file content sent.... just below the new progress bar showing smush progress.