Annie Xu gives us a few reasons why Power BI refreshes might fail:
License level: Power BI Premium license has different level and Power BI Premium capacity is shared within a Tenant and can be shared by multiple workspaces.The maximum number of models (datasets) that can be refreshed in parallel is based on the capacity node. For example, P1 = 6 models, P2 = 12 models and P3 = 24 models.
Click through for the set of possibilities.