• Sometimes, the Mesh preview and the asset icon becomes pink (c.f {}MeshPreviewAndIconPink.png{}). 

So good and bad news: this problem is not only for {{SpeedTree}} assets. I have been able to reproduce it with a classic {{FBX}} (c.f {}BugModelImporter.gif{}). 

The issue is starting from 2023.3.0a7 for the SpeedTree9 assets (since we developed and landed this importer recently), but for the FBX it's probably a really old bug. 

The {{preview system}} seems pretty complex. Basically, if I understood it correctly, there's 2 paths:

-- Sometimes your asset is being render in {{realtime}} (so you can directly rotate the asset using the left-click of the mouse). Like this: (c.f {}RealtimePreview.gif{}).
-- Sometimes your asset is a {{cached texture}} (so you cannot rotate it like the previous one, you need to click first on the texture, so it becomes a {{realtime}} scene, and now you can rotate it in realtime). Like this: (c.f {}CachedPreview.gif{}).
Not sure what determines the system being used. Though, the icon of the asset is always using the second system (a {{{}cached texture{}}}). And as you can see in my first GIF, the {{icon}} of the FBX asset becomes pink after these steps:

-- 1) Extract Materials
-- 2) Delete Materials
-- 3) Reset Asset
-- 4) Extract Materials
Only the {{icon}} is pink and not the {}{{Mesh Preview}}{}, since it is using the first system (realtime rendering). Though, for assets using the cached texture system, it becomes pink too (it looks like the icon and the preview texture might use the same snapshot? Might make sense since it's very low-res...)

Anyway, I've been able to reproduce the issue for FBX and SpeedTree assets, on all {}{{RenderPipeline}}{}. I attached both asset (realtime FBX & cached ST9 asset) to this ticket in AssetsPinkPreview.zip

It seems a problem in the texture generation system itself. As far as I dug, it doesn't regenerate a snapshot after re-extracting the materials the second time ({}step 4{} in my previous comment), so it's reusing the previous snapshot generated (right before clicking on Reset, so the pink one).