I have several reusable popup elements with several workflows.
In the workflow tab, for each reusable element, I noticed that I can only see none to few of the workflows, HOWEVER, I can still access them using the add/edit workflow button in the properties panel in the design tab.
This is a bug I faced in new workflow builder.
You can raise the ticket to bubble support and for now you can disable the new workflow builder and use old one and you can see all the workflows without missing.