SQL Server 2017 Tabular Data Model

I've created a tabular data model in Analysis Services. The model is set to update nightly from two SharePoint lists. I can't get the credentials to stick, so the nightly refresh fails.

When I go in and set credentials in SSMS, I can process the model fine. I had another admin process the model and it worked fine. I can even trigger the scheduled job and that works fine as well--regardless of who runs the job. Why won't the credentials stick overnight? Has anyone seen this? Any ideas?