If the system your building is "mathematically impossible" to explain in a way that would be expected of every other system. Maybe you shouldn't be building that system.
Perhaps you can’t perfectly explain it but you can at least understand it statistically.
For example is not currently possible to mathematically explain people’s behaviour, but there is statistical evidence and also accountability on an individual. Eg a doctor making a decision about a scan result.
The following would seem to be OK: "This model performs well in a set of tests we devised, your mileage may vary."