Happens a lot.
I grew up in a rural town with a lot of farms and former farmland.
The house next door had a driveway that was shaped like an S: it ran straight in about 50 feet, turned 90 degrees right, ran another 50 feet, then turned 90 degrees left to enter their garage. The driveway met the road on the far left of their property, and in fact the edge of the driveway was the property line.
That part of the driveway ran along a right-of-way that allowed access to a property that sat behind both houses. Our next-door-neighbor had bought that property when he bought his house specifically to prevent someone from building houses back there and running the access road right between our houses.
That rigjht-of-way was entirely in land that went with the house he bought, but there was an easement that allowed the owner of the land behind to use it.
Your land had a similar easement: that alley. It was a right-of-way that every property that bordered it had access to. Once upon a time, the deed to the property Building A is on said that the alley was part of the property, but had to be left clear.
Then the alley “ceased to exist”, and Building A, B, C, and E no longer show an easement for an alley along the back of the property.
And, my brother notes, have been paying property taxes based on that easement not existing anymore. This may be important because if that easement still exists, all those property owners are owed refunds of some of their taxes as their property is worth less. This will encourage authorities to rule the easement does not still exist.
The problem is that Building H may have had a deed that showed it could be accessed through that alley, just like the property behind the house I grew up in had a deed saying it could be accessed from the right-of-way between our house and the one next door. When they abolished the alley, nobody thought to worry how Property H would access the street.
And the new owner of Property H read the deed, and saw he has access through a right-of-way in a 8 foot strip just south of the property line.
I hope I’m wrong about that. It will be much simpler to handle if he’s just a jerk.