google-maps-v3 | Simple PHP API to use Google Maps v3 service | REST library

I am loading a map from react-google-maps-api, and then based on the current zoom & center point, we calculate the radius of the map to retrieve items within the "viewable" area of the map. However, the radius being calculated seems to be larger than the visible area.

I have referenced some existing SO threads including this, this, this.

Our map is initialized like:

I've put together a map with clusters. The idea was that cluster's color should depend on the color of markers inside: if there is a red marker, cluster is red; no red, but there is a yellow marker, cluster is yellow; no red and yellow markers, cluster is blue.

This only works as expected at specific zoom levels. Fully zoomed out it shows blue cluster, however there are red markers in there, so I expect a red cluster. When I start to zoom in and the map shows multiple clusters, most look right, but in some instances this offending behavior repeats, it will group red/yellow/blue markers into blue cluster, I expect red. Same with Yellow + Blue markers should form a yellow cluster, not blue.

According to this setCalculator function runs for each cluster individually, therefore I was expecting consistent behavior, but instead we have mixed results.

I’m trying to make my own marker on the map, but the problem is that it moves out when the map is zoomed, I read here about the fact that I need to add an anchor

Google Maps v3 custom marker icon does not keep it's position on map

I added an anchor, but the marker immediately becomes default, tell me why?