I see Only 2 option now:
1. 24 seed generated completely Randomly and Both device got the same seed. But its very unlikely
2. Ledger use pre generated 24 seed and probably due to an error both device got the same 24 seed. This senraio is more likly to me.
But again I have no any evidence.
Your have a third option:
If the device is proven authentic and the seed phrase is generated by the device,
Ledger Nano X in general or two particular Ledger Nano X devices' "
True RNG" may be flawed.
I read their
Whitepaper and they claim to be using "
True Random Number Generator" which links to this Wikipedia page:
https://en.wikipedia.org/wiki/Hardware_random_number_generatorBut since Ledger's hardware and protocol isn't partially open-source (
yet), no one can check if their RNG has something to check for malfunctioning or missing entropy sources that could lead to weak RNG.
In any case, it's recommended to contact LedgerHQ so they can investigate it since she shouldn't be using the unit itself, not just the seed phrase.