Most LOD issues never where and probably never will be fixed
Since original il2 there where some quirks with the lods so I simply put them to the max (even though most of the time I didnt have the machine to run it smooth, but better than invisible stuff)
Still some aircraft dissappear like you described , but there are some vehicles that dissappear in mid range and pop up again even on maximum settings, I hope that gets sorted out with the new engine , but with il2 you have to much objects to check I´m afraid