So in polar missions, both campaign and quick battle, my agents and tanks can't disembark the craft: they actually can't step on the craft's ramp.
(The tank also goes a little crazy and the autoshot of its auxiliary weapon only shoots 1 bullet; agents seem to able able to autoshoot normally).
Agents with a flying suit can move normally, walk on ramp and walk outside.
This with latest nightly too.
(If someone else with a very recent, if not latest, nightly can quickly try if it happens to him too).
Ok nevermind, this was because of some crazy experiment I did with polar terrain a while ago and of which I had completely forgotten until now.