There are many reasons why a workflow could fail to work as expected. In general, there are some primary checks you can do to assist in troubling issues.

Troubleshooting Checklist:

• Test with a “Fresh” Contact - After testing multiple times, utilizing the same contact can cause unexpected results with a workflow. Try deleting the contact and using a fresh contact as often as possible.
  
  

• Test with a Contact - The option “Test Workflow” in the top right of your Workflow builder has limitations when testing. Try to use an actual contract and run a live test by triggering the workflow as a live customer.
  
  

• Check your filters - Filters can be set at the trigger and action level and allow for precise triggering and actions. Without them, you may find that the workflow performs when you do not want it to. Check your filters.
  
  

• Check Workflow Settings “Allow Reentry” - Allow reentry enables a contact to be added more than once. If disabled, it will not be allowed to re-enter. When testing, it is easy to forget this, resulting in contacts skipping the workflow. Deleting the contact or enabling while testing can help.

For more information, please check out this article from HighLevel:

Getting Started with Workflows