if not mentioned b4, dunedain rangers combined cant use longshot. Then again, it's not a real problem. It's actually a good thing!
And the invisible arnor soldiers happened to me 2 once. Just re-download like all the others said, and it's good as new.
I think that you don't really have to re-download the whole mod, for me it didn't help. What did help it to set the model detail and all other unit-related settings to ultra-high, not all the graphics settings, just unit related ones.