Do you have the save so we can give this a check? Will also need it to check which polar biome map this was (and what UFO type).
For the ufo being seen in shroud, this is most likely because the top part of the ufo entered a soldier's LOS. Looks like this is one of the ufo types that goes up to 3 levels high, while the pine trees are only 2 levels high, so it's not perfectly blocking said ufo. Will need a save though to verify if this is a case or if we have an actual bug
EDIT: Need the save specifically for the ufo (the water one is easy to reproduce)