I think the query is flawed #7

There are multiple reports of incorrect results.

Querying by the lower and upper geohash range, seems to be incorrect.
As you need to query around the geohash centre point.

But the range finds every geohash between the upper and lower, lexicographically.
Which in some cases, will find geohashes which aren't actually close to the centre point and misses others that are close.

Other packages use bounding boxes etc to query geohashes, which would find the cluster of geohashes around the centre point.