Happened to me too, Trilogy ... I had to place 2 or 3 and then visit a neighbor before placing 2 or 3 more and repeating over & over til they were all placed & stayed.
...on another note, it happened to me over & over during the Weekday Warrior, too. I chopped oodles of willow trees only to have the game reset & put them all back. In the end, I only managed to get about 30 vines and then had a board full of trees leftover that I had to use my energy stash to get rid of. Of course the resets didn't happen then. FIGURES.
What in the world is going on with the resets!?!?!!!