Noticed a bit of an annoying bug with World Imagery basemaps, if you zoom in closer than 1:1500 the basemap jumps out of the correct TOC order and is all that appears on the map, essentially it moves to the top. Actually the trigger is somewhere between 1:1700 and 1:1650.
It also causes a major CPU spike and ArcMap freezes for a couple of minutes before becoming responsive again.
Currently affecting South Australia, ArcMap Version 10.6.8321