VTOL System Shutoff on 1.11 code during Mission Mode


We have a small VTOL aircraft. The other day when flight testing, the vehicle ascended up to a set way point at 60m in multicopter mode. After getting to this altitude, everything shut off and the vehicle plummeted to the ground. The warning signs from the log are shown below.

[load_mon] wq: UART4 low on stack! (252 bytes left)
[mavlink] instance 2: RADIO_STATUS timeout

We have our RC failsafe set to kick in after 0.5 seconds which would trigger RTL. Could this have possibly been triggered and then the vehicle just terminated all power?

When picking the vehicle up off the ground, it was powered on still.

Log below: