The vegetation in game will pop in/render when the player is a few meters away from the object, it seems to me there is a primary vegetation in which is dictated by the view distance and a secondary one that there is no settings to edit to fix this. I beleive the the below posts are the same issue that i am, its very distracting and immersion breaking. This happens on both vanilla, modded, as well as the standard branch, profiling branch and dev branch.
https://forums.bohemia.net/forums/topic/193673-tanoa-grass-lod-issues/
https://www.reddit.com/r/arma/comments/4w9asa/is_anyone_else_getting_severe_lod_popping_in_arma/
https://www.reddit.com/r/arma/comments/5sbki8/grass_popin_lod/
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