Vector, when it reallocates memory, it invalidates references.

https://www.ultimatepp.org/srcdoc$Core$Caveats_en-us.html

I don't think there is a workaround for this and you are not supposed to long term store references gotten from vector, just store them for a short amount of processing, until the next operation on Vector.

I believe if you need to store references the correct way is to use Array.