Auto retention label policy does not work in SharePoint Online

I have created an auto retention label policy and ran and tested it in simulation mode two weeks back, but when I run the same policy with the same query in simulation mode, it does not give any matching result; always it comes with 0 matches found. However, when we test the same query in SharePoint Online search, it gives a result. The policy is completing on time; sometimes it takes hours to days to complete, but sometimes it completes on time as expected. What could be the reason? Are you also facing similar issues?

Thanks!