It’s seemingly better that when I created the OP, but cases such as hosseinimr93’s depict a scenario that should render many more results than it actually does. I just retried it with the same results (4 resulting posts).

If you search for the keyword bitcoin by user acroman08 over the last 300 days, you only get 1 result, whilst manually searching for the term over your latest 20 posts renders quite a few more results.

Popular keywords not filtered by user render better results in appearance, but they may be returning a subset of the results. Could be a corrupt index (multiple) thing, but that’s just a guess on my behalf.