So a quick summary for the noobs like me means mode 3 has caused the OP to send the wrong commands to the drone?
Isn’t this part of most pilots check when first launched - about 6’ up? Or is it capable of switching modes during flight??
That's totally correct...
The throttle stick command correlates to heading speed seen in the chart below...
... and the elevator stick command correlates to height... & there it's easy to see that the OP constantly applied descent commands...