I can’t assist with Nanite specifics as I don’t use it. Some people went nuts on the forums with various fixes for their situations. Make a backup of your project (as always) and you could try a few of those posts
Heavy Nanite Bug. Mesh Disappears at Distance - #10 by July014
Since they used the city example project as example, you’d think that would be close enough to your situation. They had the problem of certain details collapsing (tree leaves, branches etc.). The similarity I see to your models is that the wireframes are basically modeled branches.