Query Store bad performance and cleanup doesn’t work

Hello, 

We have SQL Server 2016 (SP2-CU14) , and a lot of problems on Query store, performance and cleanup.

Regarding performance, in short, any of the reports  (ex.: Top Resource Consuming Queries) are extremely slow. We tried to create plan guide, but not work.

About cleaning we have:

max size: 10GB 
flush: 15 min
statistics collection: 1h
Capture mode: auto
size based cleanup mode: auto
Stale query Threshold (days): we tried 7days, 3 days, and now had 1day

Does anyone have any suggestions for troubleshooting or resolving the problem?

Thanks 

Doug