One way find all the workflow instances that have run can be found in Tasks>Common Search, and select the workflow you are having issues under "Search by Workflow". This will show all the instances that have ran for this specific workflow. There is a few things to check:
1. Did Workflow register the instance that ran for the times that it did not save into the database?
- If not, you need to establish why the workflow wasn't triggered. How are the workflows started? If it's by starting conditions, make sure that they were satisfied.
2. Do you see any instances that shows a warning (yellow triangle) or error (red cross). See any Workflow Status as terminated?
- Check what the warnings/errors are and see if they can be resolved.
I also recommend taking a look at our Workflow Troubleshooting section to help you try and reslolve this problem. Hope that helps!