WP Smush Pro goes to outer space after x attachments

53 of 104 total attachments have been smushed

And then nothing. The progress bar has stopped, the spinner's still spinning, but no more progress.

Three questions:
1> What is the safest way to get it to start again
2> Is this a PHP timeout issue? My timeout's pretty high...like 180s
3> What is the solution
Thanks,

Steve