It is a side-by-side comparison of OSM data from 2012 (left) and the current OSM data. In my local area the difference is massive: the 2012 data has some roads but that's about it, no buildings, house numbers, etc. That's all present on the 2022 version (disclaimer: partly because I spent several months walking around mapping things with the StreetComplete app [1]).
For me it isn't down, just taking a very long time (multiple minutes) to load the 2012 data.