Is this a bug? An enemy is not showing up as a red dot on the overview map, and never
shows up inside the grid, either. He shoots at me, but never hits me, and I cannot find him even after an arduous sweep.

JA2. I'm in Grid G12. There were nine enemies, with only one left.
A very tedious sweep of the entire map does not find him. Sweep again, and in the lower-right hand corner, the game goes into "Alert" mode---by that I mean suddenly you're in combat, and have to give individual orders to each merc.

I walk them into the lower-right corner, even more tedious now, because it's dependent upon Action Points. No matter where I go, it stays my turn.....no red bar for the enemy turn ever appears. If I walk to the west and hit the road, I come out of this tactical mode. If I walk far enough north, I also exit tac mode.

Did this numerous times, and finally the game started showing the red enemy turn bar. I can hear shots being fired, but the enemy never appears on the map, not even as a red dot on the overview map! No matter where I walk or stand, I can never see the enemy. No matter how many times he shoots, I never get hit!

This is aggravating beyond belief. Tried saving and reloading, didn't help. Tried exiting from this Grid square, and returning, big mistake. Reinforcements have arrived, and slaughter my wounded mercs. The entire Grid Square G12 is hostile territory, no where to run and patch up my mercs. This sucks so bad.

It can happen rarely, does enemies run out of the visible map by a few fields but didnt flee out of the sector.
What u can do:
-Start autoresolve the fight
-Leave the sector, leave the gametime on pause and break the travel. U directly return into the sector. The enemy should now have another position.

Edit:
Leaving an ongoing battle can cause the moral dropping. This is more harmful when u leave a town sector during it is under attack. The support (and so its income from the mine) can drop significantly.