14.6 ORCHARD ROAD: A hex containing both orchard and road symbols (such as 23Q8) is actually a tree-lined road. Entrance of such a hex through a road hexside is identical to movement along any road. Hindrance rules do not apply to such hexes if that portion of the LOS from firer to target within those hexes never leaves the confines of the road depiction regardless of the relative elevation of the firer/target; in such cases, the -1 FFMO DRM applies to Infantry using the road to move. Otherwise, orchard roads are identical to orchards in every respect.
It looks like the last two orchard hexes have roads without trees in them and the LOS is travelling down those roads. Thus O5 is the first orchard that doesn't. The rules here only speak of hindrances, not obstacles for road portion. Presumably the in-season tree branches 'arch out' over the road in M5, still creating an obstacle, and blocking the LOS, as you say. There is some room for doubt.