This is a duplicate bug report, but the first time this bug was reported that I know of was last December, in the post linked above, and the BETA patch still hasn't fixed it to this day.
Phenomenon: Inactive units are not attacked, and when both combatants remain stationary the firefight will suddenly end within a few turns.
How to generate this bug:
I could repoduce it in one of two ways, the first being the easiest, commanding my units to assault into the enemy's hex and the firefight will end within a few turns - as long as neither side is incapacitated or wiped out, they will no longer engage.
For the second, create a copy of any scenario, place all units in the scenario into a column, set SOP to no relocate and ignore losses, and the battle will also end in a few turns.
Two Real Cases
Real case#1 : When my defending units dig in in a position at the north in the Panzer Forward scenario, the Warsaw Pact units commanded by the AI approach the VP below from the south, and my units fire on them as they move. However, when the AI seized the VP they stopped moving and my unit stopped attacking them, the dashboard showed that my unit had all the parameters to allow it to fire on the enemy.
Real case#2:the enemy spotted in the same stack did not engage my unit for 3 whole stacks
When I commanded the Warsaw Pact and had all the units carry out the order to assault, they stopped fighting within a few turns after they had assaulted into the enemy's hex.
I know these infantry ran out of anti-tank ammo but what about their rifles? Have they turned into twigs? Not to mention the Soviet units I used for the assault, and besides what about the other two stacks next to them?

AND Stop asking me if they have LOS! This was the explanation for the first report of this bug, which was then left until now...

The devs told me that LOS is not the same as LOF and that it is not the same as a weapon having the ability to fire at the enemy, and in some cases I totally agree. However, Jesus Christ, are we playing a game setting in American Civil War era?
Would a 16" rifle cartridge have an effective range of less than 500m?
Isn't a 125mm 2A46 cannon having LOS within 500m the same as having LOF?
So I'd like to know what else I can use to describe this West German mechanized infantry and East German T72M1 in my screenshot as being able to spot each other but not engage in combat, other than a bug?