When you reduce the radius of a cluster of map points or disable clustering at a particular zoom level, this may result in too many points for your browser to handle quickly and the map rendering may start to slow down. If this happens, delete marker labels for objects with most points (of for all of them) - this will dramatically speed up rendering.
To remove marker labels for a feature, simply click the "trash" button next to all the required fields in the map properties
Marker column:
