I noticed this as well. I think that ther is a bug with tha LAV-AT in that it is missing it's IR optics. I built a simple mission in the editor with a bunch of Syrian vehicles at one end of the map and some LAV-AT's, TOW humvees an Canadian LAV TUA and a few unarmed vehicles at the other end. The two sides are about 1100 m separated. The weather is clear. I ran one setup at 11:00 and one at 23:00.
In the mission at 11:00 all the TOW equipped vehicles immediately begin spotting the enemy vehicles. The unarmed vehicles spot the enemy fairly quickly as well.
In the night mission the TOW humvees and the LAV TUA have no problem spotting the enemy contacts real quick. The LAV-AT never spot anything. LOS for the LAV-AT stops at 400ish meters. The unarmed vehicles (or rather the dismounts) have LOS of approximately 1000m, which I assume is the limit of the night vision gear being modeled.
LAV-AT test day.btt
LAV-AT test night.btt