Col Jacques Baud has documented that those "Russian troops" or "little green men" were Russian speaking Ukrainian nationals who pulled off their insignia and switched sides.
It’s very very tellingyour go to source was a Russian disinfo guy.
Col Jacques baud per Wikipedia: He has been criticized for his relaying of several conspiracy theories, his denial of the Syrian regime's responsibility for several chemical attacks and for his pro-Vladimir Putin positions, including through the sharing of disinformation during Russia's invasion of Ukraine