I would suspect that updating firmware was not the culprit or it would be happening all the time.There is another thread where someone indicates that the most recent firmware defaulted his setting to Hover. Seems like the likely culprit, and a bad, perhaps not intentional change in the firmware.
For almost all flying, RTH is the only Loss of Signal option that makes any sense.
It's for that reason that it is the factory default setting and always has been.
It does not change unless you change it.
And if you change it and then update firmware, it's likely to revert back to RTH.