FrSky have already confirmed the *possibility* of a clash, albeit a very small one.
This leaves two potential situations:
1. there was a legit clash and both radios had the same (non-zero) GUID
2. there was another issue which set the GUIDs of these two systems to zero (quite possible -- as we know, interrupted EEPROM writes in microcontrollers can cause data-corruption/loss -- that's how the Futaba zero GUID situation came about and it's also why JR and some Spektrum radios develop the infamous "Backup Error" message if the power is disconnected while they're shutting down.
It would appear that if it's a design error, FrSky is in some very elite and well-heeled company
But, as LV Martin used to say "It's the putting right that counts".
RCModelReviews.com, just the facts.