thanks for the report - but without a steps-to-reproduce we can't really fix the bug.
is this always happening to you on this map? does it always happen under some special circumstances?
The invisible aliens actors are happening because game is out of sync. Any action with camera movement lags, typically on aliens shooting on long distance. As result i see message about wounded soldier long before alien which wounded him even have started to move and movement of previous alien is shown (bullet in flight).
I think that bugs with dead aliens left standing or invisible aliens is related because it's often happens on maps with wide space like dam or farm.
To reproduce, simply open GAS STATION maps or DAM, have one of your agents spot an alien at least a few screens away, and let them shoot at you for a few turns.
You can force the issue on DAM by staying around the landing pad and playing sniper. As you move your soldiers around the aliens will move around on their side. Eventually you can get one that will seem to be "stuck" partially between two tiles, really he's invisible and moving and shooting.
Force the issue by staying on your side of the Dam map and playing at sniping. You will have an invisible actor in no time.
