Hi, I have the same issue.
It looks like inserters only try to grab stuff from delivery drones if they don't already have a machine/chest/belt to grab from. So inserters inside production lines should be fine, only inserters grabbing from "empty" tiles (e.g. at train stations) should be affected.
My guess is that this happens because the delivery drone uses the CarPrototype. Inserters can interact with cars, so they can interact with drones too.
Some workarounds I found so far:
- Replace inserters at train unloading stations with filter inserters (obviously this won't work well with generic dropoff stations or circuits, but it will at least prevent other item types from getting mixed in).
- Replace affected inserters with AAI Loaders - they can unload from trains, but don't seem to interact with delivery drones at all. Not sure if other loader mods will work, my guess is that anything which uses the builtin loader entity should be fine (so e.g. Krastorio loaders are likely to work, but things like Miniloaders which use invisible inserters under the hood might have issues).