Flight mode: unknown error

hardware: PIXHAWK MINI
firmware: PX4
QGC: v3.1.3

I sometimes get the error message below when I connected pixhawk to QGC with USB cable.
When this message is shown, “Flight Mode 6” becomes “Unknown: n”.
This error is not always; almost at 1/2 chance when I connect them.
When the message is not shown, I can see the value of “Flight Mode 6” properly.
I reinstalled firmware a few times but this phenomenon has not been resolved.
Does anybody know the reason of this error?

In addition to it, when I connect the battery to my vehicle to fly. I always need to reconnect the battery. Because at first connecting, LED of I/O B/E keeps blinking yellow and rejects arming, and at second connecting just after the first connecting, I/O B/E will stop blinking and I will be able to arm.
I do not know if these problems have connection with, would you please help me with this error too?

Which version of PX4 is this? Does it only happen with USB power?

Hi dogar, thanks for your comment.

PX4 version is 1.5.5.
I don’t know if it only happens with USB power, because I haven’t succeeded to connect QGC wirelessly.

This problem seems to have been resolved by replacing GPS module, although I don’t know how they relate. My GPS module had hardware error and 3DR gave me a replacement. After replacing GPS module, this error stopped.