It's strange, I have a Galaxy S5, not rooted yet :p, running Lollipop 5.0: There, the internal SD path for OsmAnd folder is /storage/emulated/0/Android/data/net.osmand.plus (actually I'm using a nightly build of v. 2.3)... and it's accessible even with non-stock File Manager (i.e. Total Commander). Anyway, did you try to access it with the stock file manager? It looks like it has some "special access right", being also capable of writing the external SD (yes, you can't access external in write mode from Android, with third-party file managers unless you root, and BTW this makes me going nuts :-/)
Folder Path should be the same also in LP 5.1, but i know there could be different mappings of the same folder inside the very same cell phone... and with different access rights too!
Just have a deeper check, but I would not be surprised if Huawei decided to screw up the things more than Google itself did...
Cheers,
Max