As you may have read I ran into the same issue as Oliver the other day after installing a Realsense module on my bird (Yea you read that right) and after manually turned off the GPS to test the IPS in my living room I couldn't re-enable GPS and enter flight mode.
Following Oliver's guide downgrading to 652 and back up again to 784 did not fix it for me, so I submitted a ticket at Yuneec and got the solution first thing this morning with this reply
Hi, the system still thinks it is indoors since you told him so, you may need to wait a bit longer outdoors. what you can try is also, Go under settings, turn on an off the manual mode, 2-3 times end by off, then go under GPS switch and turn this on an off 2-3- till it is on.
Simple enough took the drone outside where it belongs acquired GPS ticked the switch on off a couple of times and I was airborne again.
Following Oliver's guide downgrading to 652 and back up again to 784 did not fix it for me, so I submitted a ticket at Yuneec and got the solution first thing this morning with this reply
Hi, the system still thinks it is indoors since you told him so, you may need to wait a bit longer outdoors. what you can try is also, Go under settings, turn on an off the manual mode, 2-3 times end by off, then go under GPS switch and turn this on an off 2-3- till it is on.
Simple enough took the drone outside where it belongs acquired GPS ticked the switch on off a couple of times and I was airborne again.