Negative altitude in Loiter mode. (with GPS for YAW)


I am attaching two logs.
(You may see an SSL security warning, but don’t worry, it’s safe).

They are flight logs from the same place and same time,
On the first flight, I had an issue with the aircraft slowly climbing without any radio stick-inputs (first.bin).

But looking at the logs, Alt and DAlt seem to match.
Also, the altitude is in the negative zone.

On several other flights, including the second, there was no problem. (second.bin)

What could have happened?

Note) I’m using GPS for YAW, and GPS as the source for EK3_SRC1_POSZ.

Thank you