Unable to Arm in Loiter - Waiting for error messages

I’m struggling to understand why I wasn’t able to arm in Loiter mode the other day.

Here is the .tlog and the .bin log files:
NoLoiter.tlog - Google Drive, NoLoiter.bin - Google Drive

Around 5-7 minutes in, while on the ground, I switched to Loiter mode and the aircraft will not arm. In the telemetry log I see that there is a pre-arm check failure, but it won’t tell me what that is, all it says is: “Prearm checks failing Waiting for error messages…”

Later in these flight logs I also attempted to switch in to position hold, but still had the same issues. I’ve dug through these logs quite a bit, but have been unable to see why it wouldn’t let me arm in these modes, but would let me arm in Stabilized.

If you’re able to help me out could you walk me through how you went about finding what the show-stopping error is so that I can find it myself in the future? I really appreciate the help! Thanks!

That’s some old firmware.
Prearm-need position estimate. 8 sats and an Hdop >1 is not going to do it. Wait…

In the docs it says that

" [The vehicle can be armed in Loiter mode but only once the GPS has 3D lock and the HDOP has dropped below 2.0.] (Loiter Mode — Copter documentation)"

So I assume that even though HDOP is >1 it is still <2, and therefore should be able to arm, right?

No. It’s not that simple despite what that says.