Descent stops at 50m

Ok, dumbass question.

Ran autotune on a rig, and completed without any issue. Next, planned a 6 min map mission with 4 legs, at 100m Alt. Mission runs and returns to home point, rig descends from 100m to 50m, beeps, and stops descending. Same results at the finish on two additional flights.

Arducopter v3.3.3

What am I missing? LOL
Thanks!

Screenshot of your mission and some logs may help a LOT.

Uhmmm, NOTE TO SELF!!! LOL

Confirm RTL_ALT_FINAL is set to 0(zero). Duh!