If any workflows associated with an End User's Solution Instances are not working as expected, it is possible to go into their list of Solution Instances and underlying Workflows in order to inspect the logs for any workflow runs associated with their Solution Instances.
This can be done by going to the Users section of your account, filtering the user and clicking on 'See instances':
For any of their Solution Instances you can then click 'See workflows':
And then 'Debug workflow':
You can then inspect the logs for any failed / successful runs of the workflow for this End User's Solution Instance (for more guidance on working with logs see our main platform Logs and Troubleshooting guide):
Note that here you are looking at a read-only version of the End User-specific version of the Workflow and if you want to make corrections you will have to return to the Source Workflow found in the original Project.
You will then need to update and publish the new version of your Solution as described in Updating Solution Instances.