The only time I have seen a problem with a RAID 1 array in the last 20 odd years was when a disk physically died and someone pulled the good disk rather than the dead one (we were able to recover all their data from the 'good' disk and managed to get them to set up a valid backup system).
Unfortunately all small NAS boxes use what is known as a software raid, where the operating system does the necessary processing and can be a problem if the parity information is damaged in some way. Once the data structures are damaged or lost, data recovery becomes a long slow process and full recovery is most probably not possible.
In my old company (I am now retired) we had signs saying 'any data that you do not have at least two other copies of is not backed up', my department added to that with 'and a third tested copy held off site'.
I am very sorry that you appear to have lost your data, I think we have all lost data at some point, but you must consider the value of the data against the cost of possible partial recovery. That is something I can't advise you on.