Rate limit strange behaviour


I noticed strange thing.
In the end of every hour all requests to /api/x/store start to get 429 in response.

Metrics looks like:

Version 9.1.2
Rate limit - 20k (more, than actually requests count)

Is it kinda bug?
Was it fixed in v10?

also, I see in a stats page 500к requests accepted and everything else was dropped. Is it on-promise restriction? Can I set more than 500k per hour?