I would check with whomever is in charge with site maintenance for that area as it sounds like they may be switching over a main power source around that time every night. If so, and there is a temporary interruption in the main power source, some reasons for only 1/2 the trailer or complete trailer going out could be:
All trailer with no power = AC out and low battery charge or no charge would result in loss of DC power as well
1/2 trailer out = all AC went out but enough charge on batteries to power DC lights
In either case it sounds like the batteries may be due for replacement.
I'm not saying this is the case but trying to logically think this through, the above makes sense to me.