xcom-2
Cover/line-of-sight appears to work slightly differently in XCOM 2. For example, take this situation:
In XCOM:EU, my unit would be able to attack the enemy in this situation (see for example this explanation of how LOS works in XCOM:EU, under side-stepping).
However, as you can see, she can't attack him. Why? How has cover/LOS changed in XCOM 2?
After getting your squad together, if you rename your squad member in the customization settings, if you change the name to a specific name the game will make it a "special" XCOM hero. There are two others you can get as XCOM heroes, all discovered through the default.ini configuration settings:
;SUPER SOLDIERS!!
;Sid Meier BodyPartTemplateConfig=(PartType="Head",
TemplateName="Supersoldier1_M",
ArchetypeName="Head_Supersoldier1.ARC_Head_Supersoldier1",
Gender=eGender_Male, Race=eRace_Caucasian, SpecializedType=true)
;Beaglerush BodyPartTemplateConfig=(PartType="Head",
TemplateName="Supersoldier2_M",
ArchetypeName="Head_Supersoldier2.ARC_Head_Supersoldier2",
Gender=eGender_Male, SpecializedType=true) ;VanDoorn
BodyPartTemplateConfig=(PartType="Head",
TemplateName="Supersoldier3_M",
ArchetypeName="Head_Supersoldier3.ARC_Head_Supersoldier3",
Gender=eGender_Male, SpecializedType=true)
So basically, you just need to rename your squad member to either:
In order to get an XCOM hero!
For reference, Peter Van Doorn is a famous NPC you can rescue in XCOM: Enemy Unknown.. Sid Meier is a famous developer who is the creator of the Civilization series and director of Creative Development for Firaxis Games. Beaglerush is a famous XCOM streamer and youtuber.
Hold Ctrl while selecting tiles to set a specific movement path.
Best Answer
Since no one (other than Firaxis) can know for sure, here's my interpretation of your picture:
The soldier you're trying to target isn't standing in the open door, but next to it. He's standing in the same line as your soldier, and the full-cover-box you can see behind the doorway.
I think it's that specific box that is blocking your LOS. Even if we consider that your soldier sidesteps (so let's assume she's standing one tile to her left); it's possible that the slight elevation of the train cart combined with the angle of the box (relative to how your unit would see the enemy soldier) leads the game to decide it's not in LOS.
That being said, this is just a guess. I remember being in similar situation and seeing my target. The only thing different here is that box, which is why I'm thinking that's the reason.
Edit
For those who argue that the enemy (model) is in sight of the soldier, therefore it should be targetable, keep in mind that the game calculates based on the tile a unit is on, not the actual visibility of their character model.
I find that units in cover really cling to the cover, or try to pop out their heads, and it throws off your vision on where the tile is located. If you look at OP's picture, you'll see how much difference there is between the enemy's body and the actual center of the tile they're standing on.