A friend of mine was bow hunting sept 2018 and came upon a meth lab on USFS land. he took pics and gps coordinates to the USFS office and reported it. as of a few weeks ago the meth lab was still there.
....... Anything short of having a surveyor out there will not get you to be able to tell exact land boundaries any closer than + or - 20 feet or so. They will be even less accurate.....
On my farm in Virginia the county's GIS map is wrong by 150-200' for most of the border, when compared to my surveyors' plat. You can't expect great accuracy from OnX or any other mapping program that depends on the county's GIS data.
If that "hunting lodge" is nowhere near a private property boundary then you should definitely be suspect.