The rangeSlider computes the min and max range based on the first 1000 facet values. Algolia was designed for speed rather than exhaustivity and this min/max range calculation is a result of that design. This is a limitation that we have been actively working on, and if you are not using the latest versions of our libraries, we recommend you upgrade so that you can benefit from the latest optimizations.
Widgets can be customized: the rangeSlider widget has a min and max input that you can manually change, as shown here.