There are some quirks with how to build a perspective for your kubernetes report.
If you are building a perspective for a classic kubernetes report then you'll need to use the containers > kubernetes asset:
If you are building a perspective for non-classic kubernetes reports then you'll need to use the Kubernetes (for FlexReports only) asset:
If you try applying a classic kubernetes perspective to a non-classic report then all assets will be unallocated. Same applies when applying a non-classic perspective to a classic kubernetes report. Also, neither of these perspectives can be applied to regular cost/usage reports.