Pixhawk 6c "pos_horiz_abs" consistently off with stable position values

Hi all, I’ve been working on an autonomous indoor drone using Marvelmind beacons and have had much success except for one single error that keeps popping up. I am using ArduCopter 4.5.2 with a PixHawk 6c, and transmitting the position data from one of the two beacons via UBlox. So far, I have been able to connect the Marvelmind beacon to transmit position data successfully, and I am using the GPS for position, altitude, heading, and velocities. I have two beacons set up on the indoor drone, and the beacons are set to be paired from the Marvelmind software interface to generate a heading without using the magnetic field seeing as that may be unstable during indoor flight (flying next to steel warehouse frames). Only one beacon needs to be connected to get the full set of data. This bit was tricky but I’ve made it so far.

What I need help with is that the pos_horiz_abs flag is consistently triggered to off - this can be seen from the EKF status window. I am not sure why this is happening as the value for the accuracy of pos_horiz_abs (which I can not recall the name of at the moment) stays under 0.6, where the threshold for trusting the position has been set. So all of the bars in the EKF window stay very close to 0, but the flag is still triggered. What is also strange is that the position the drone is receiving is also quite stable and accurate, and I have changed many parameters to try to loosen EKF into trusting the position blindly.

I am hoping that one of you knows how to diagnose this issue and figure out where and why the flag is being triggered. One small caveat is that when the EK3_SRC1_YAW is set to none (0) instead of GPS (2), the flag finally turns to On after around 15 seconds of flight, and the drone can be flown in PosHold and Auto modes - hopefully that’s indicative. In this flight scenario I am under the impression that EKF3 no longer receives any yaw data, and yaw seems to no longer be stable either.

Here is the parameter list:
indoordrone.param (17.5 KB)

Here is a log from a flight with the drone where the flag is Off consistently: