I did google migration of dragonflies .
I found out that this is an ongoing mystery.

There is a website that asks for citizen assistance.
It is a partnership between Canada the Us and Mexico
The web site is :www.migratorydragonflypartnership.org/

When I did google I found a number of PDF articles of interest.
You can also find interesting info on You Tube.
It was interesting to note that hawks feed on them during
their migration south.
They also survive as eggs or nymphs in ponds in winter.
Joyce B.
Enfield Center