This has also happened quite a bit for me. I will tell a unit to go to a certain place that will take several turns to do so. However, the next turn, it centers on that unit, and asks for commands, as if I never told him to previously go to the spot I chose. Very annoying. I think the units were in the jungle most of the time I did this, but I'm not sure if this has anything to do with it.
m2

Are the units passing by any enemy or friendly units with "cancel orders for enemy/friendly unit" preferences checked?