Hi @JFarmer,
I thought about the assignment changing so I experimented with updating the Path Assignment before/after the Send Email Step, but both produced the same results. The issue was not that it was sending to the wrong user, it was that it was not showing any email in the To: line where the Arcade expression was specified, but it was sending to a CC that was just my email address as static text.
I was not getting anywhere with this so I ended up opening a case with Tech Support. There was not a clear answer to why the email was not populating. I can run the step as expected as an Administrator user type but any other user role will not evaluate the Arcade expression to populate the username's email address. The support tech suggested I review the Portal and Workflow Manager roles and privileges for clarity.
After that recommendation, I could not find any privileges within the Workflow Manager roles that would cause the issue I'm having. So, I started looking at the Portal roles. Most users using Workflow Manager are Publisher roles. So, starting with a using having an administrator role, I began turning off privileges until the step did not run successfully.
The conclusion I came to was that users without 1 Administrative privilege were not able to access a user's email address. When I enable the "Allow members to view full member account information within your portal" privilege, the step works successfully for the users (Custom role is Publisher with that admin privilege enabled for Workflow Manager users.
My assumption is that the users without this privilege enabled are not able to retrieve the user's email address, which is why the To: line in testing were showing up blank. I do not know if this issue is unique to the Portal I am using, which to my knowledge is a straightforward, federated Portal install, or this limitation might be more widespread.