Hi Ali,
I'm not exactly sure what that has happened, but if the master objects are all TIFF files, then it's possible that something timed out before the derivatives were created.
You could try using the digital object derivatives regeneration task - see:
This task has a couple options that might be of use to you as well. For example, you can use the --slug option to target one specific description at a time, or the --skip-to option if the task times out, and you want to skip those files that you know have already been successfully generated.
If that still doesn't work, then one possible follow-up step would be to take a look at the PHP Execution limits in your installation. It's possible you can extend the amount of maximum time used for a file upload, or for the execution of a script. This might allow the derivative creation process to complete as expected. See: