Repro:
log in with an alt and teleport both to 2000m (or anything above the coarse location maximum of 1020m)
if both are at the same height the "same height" regular dot is visible on the minimap
have the alt fly upward
=> the alt's dot turns into an X even though avatar location data is available through its LLCharacter instance
Microsoft Windows 10
Fixed in R12.4 (Beta 1)