How does Import Query Mode refreshing work?

I think the behavior you're observing with up-to-date data in Import mode tables, despite the "last refresh" in Power BI Desktop showing an older date, is likely due to a scheduled refresh in the Power BI Service.

While Import mode datasets require manual or scheduled refreshes to stay current, the refresh schedule configured in the Power BI Service make sure that the data remains up-to-date in the published report, even if it appears outdated in Power BI Desktop.

This discrepancy may happenbecause the "last refresh" in Desktop reflects only local refreshes, not those performed on the service.

Direct Query tables, in the other hand, fetch real-time data directly from the source every time the report is loaded.  Another thing, if a refresh schedule exists, the data is likely being updated automatically.

Check this link it can help you Power BI official documentation on scheduled refresh and hybrid datasets to better understand these behaviors and configure your dataset in a better way. If all tables are necessaryfor Import mode, you can improve performance by switching from Direct Query and make surescheduled refreshes are in place.