SSRS report slow on initial query of the day
Per the article you provided, give this a shot for another potential workaround:


On the Reporting Services server, modify the RecycleTime value of the rsreportserver.config file, and time this out so a 'recycle' at the app server level of RS occurs just before the start of the regular business day every day - like an hour or so before any production RS reports would typically be run.
Then setup a small dummy Subscription report to run every day at the same time—ensure it has enough time beforehand though for the RS app 'recycle' to complete. Running this non-production small dummy report as the first and initial report each day after the RS app server 'recycle' completes should ensure RS app server stuff loads up before any production reports are run, and production reports shouldn’t experience the problem.


This way your Reporting Services app server recycle operation happens every day at the usual and designated time per the value you set in the config file, then right after that happens (giving ample time for full completion) the dummy report runs before any production reports run for the day, and then every subsequent report for the next 24 hours runs as expected without needing to wait for the RS app server post 'recycle' load operations to complete. You also could leave out the PowerShell scripted solution altogether as well if this works.