I've noticed the same and offer this solution, although it is not ideal and requires the same setup I have. Until there is a means to either specify an interval for when app report update occur (that sounds reasonable) or the app reports update every X minutes/hours by a known or default value, I've employed this solution.
The setup is to have a single policy per device. I've noticed any time you update a policy for a device and then query application reports, an updated device report will have been forced. It might take a minute or two, but the device will have the updated power management events, display state, wifi, etc... whatever app reports you have enabled.
With this, if you needed to see updated device reports either at set intervals throughout the day or perhaps only upon request, you could intentionally change any policies for any device in a benign way - I'm looking specifically at 'funDisabled', which toggles the easter egg game in settings. Pretty harmless, although changing policies often will thus bump the version often, which is probably not an issue either but something to consider.
So whenever you have need of the device reports updating, intentionally change the policy for a device.
It's cumbersome, perhaps hackish, but as we all know, clients care only for the results. Perhaps a better solution can be found going forward, but this one works for me.