Wp-Smush Pro stuck on a particular file

I have been trying to Bulk Smush and it has been going well. I have 34K images. In last 6 days, Smush has been able to process 30K images but for last 2 days, its stuck at a particular number. I read at the forum and probably it is trying to find a file which may not be there or some such thing.

How do I know the exact file where it is stuck ?

Many thanks
Nandan