Does anyone know if there are any reported bugs or issues with this mission?

Upon getting access to this mission I have now spent an incredibly frustrating amount of time trying to complete it with no luck. I have looked at the guides on Youtube and seen that you have to get up onto the crashed monorail where you install the MILA. I have been up here on this monorail and the marker for where to install the MILA is not there even though the location is. When I get to this point, on my map the quest marker is pointing in the total opposite direction. My marker is right next to that Faneuil Hall place. Up on the monorail is actually a little bit away from Faneuil Hall. My PipBoy tells me this mission is linked to the Commonwealth bank but I have been over this building so many times and there is no clear way to get to where I need to be from here. In fact I'm not even sure where I am supposed to be as if I follow the marker it just sends me round and round in circles. If I go into the bank it tells me to go back out. Then when I'm out it just keeps pointing up to the top of the bank building. I can find no way to get any higher in the bank than what you can from the inside. There are no roof access doors etc. As this mission is integral to the main story I need to complete it and it's really annoying me now!

If it is the one I am remembering, I missed another elevator I needed to go in that was inside the building. It took me a while to figure out, but eventually I found one last elevator that took me to the mila location.

If I recall, the door is part-way up the building.

If you don some power armor, you can drop down to the quest marked door from the flyover...

Since there are a dozen of locations these MILA quests send you, you are probably not in the right spot if the quest marker is far away. The game doesn't take into account that you could be the right place, just wrong cell at the place, but because the MILA site is outside (just further up the building) and you are standing inside a loading cell at the bottom of said building, the game will think it has to send you out. If you are relatively sure you are in the right building, just find your way up and up and up, and eventually, you will get the spot.

A few of these missions, can be frustrating, because some building are connected by walkways further up. So when you think you are in the right building, it could also be the one next to it

There is the Weathervane: Broken Monorail and Weathervane: Commonwealth Bank missions. The Commonwealth bank one is pretty straightforward with it being on top of a building and just requires you to go up an elevator. The Broken Monorail one is in a Monorail that is suspended in the middle of the air. If you have the Garden Terrace location unlocked, then it is easy to get to. There are some stairs on the side of the building with planks going into the monorail or you can just drop on top of it. If it is by the Faneuil's Hall, then it is the Commonwealth Bank mission. If it is Northwest of Faneuil's Hall and almost by the Northern river, then it is the Broken Monorail.

Go up into the Haymarket Mall building, there is an external exit a ways up in it that will take you right into the broken monorail and hence to the marked MILA drop location.

When you get into the building, you can access the monorail carriage from the floor that it is level with...use the walkway outside of the building.

Did that recently and i must say i enjoyed it , it leads you too all the nice hidden places

Yes I went around in circles doing some of those..

Spoilers below

For some MILA quests when I finally got there I found that there was more than one path to some of those spots.

Trouble is the start point of the eventual path that you take for the ascension can be a long way from the actual target.

Anyway to get to the monorail one you can go through haymarket to get to Garden Terrace or drop from the motorway above. Access to the motorway is from a long way away to your target.

You can access Garden Terrace from other paths.

Once discovered you can fast travel to garden Terrace.

Seeing that you have consulted video hints a short video showing the direct route below.

Also you should be able to see the target from the ground using a scope.

https://www.youtube.com/watch?v=6A9LcncRMt8