We recently had our GIS Server crash over the weekend and when it came back on board we noticed a difference in our Web Services. After some trial and error I found this pattern:
When we use - gisvm04:6080/arcgis/rest/services
Our map services don't need a Token and use the Web Tier authentication like it use to before the crash
When we use - egis/arcgis_internal/rest/services
Our map service needs a Token authentication.
After some research it looks like it might have to do with our web adapter - but I'm not 100% sure.