I've updated several Assets Sources on my production site. I've exported / imported the database from production into local - the new Assets Sources are in place but the asset thumbs are now missing.
How can I get Craft to re-generate these please?
Go to Settings > Clear Caches. Should regenerate them all from the new source.
My basePath was wrong in my config (due to a DropBox syncing issues). Once I corrected that and cleared caches, the asset thumbs reappeared.
I've had this issue before, and it was always either: