UE4.9 does not hide last LOD - speedtree

I am having a similar-ish problem but in reverse - my instanced speedtrees work fine in all cases, but when I enable the hierarchical LOD feature in the World Settings, my individual speedtree actors break (that is, the trees I drop in as individual static meshes in the main play area, rather than paint as foliage on the periphery). The scaling, wind animation and (probably) LOD settings go wrong, and some meshes around them are also affected (possibly some borked shadows - i.e. the lawn beneath the tree, which is a static mesh).

e.g. first picture is as intended (bar the over-bright foliage which is the subject of another question/bug report), then the other pictures are the same scene viewed from different positions.

I’ve reimported the trees in question with both the LOD for painted foliage and the LOD for individual actor settings selected, with no change in effect.

These are just standard speedtrees from a standard package on sale - White Birch, American Elm, London Plane, Douglas Fir, and some grass, I think.

Any suggestions? Turning off hierarchical LOD is a fix but I’d like to have the option of HLOD.

(This isn’t letting me add images for some reason so here’s the links)