as it looks to me, this is what happened :
using the newest versions of everything (factorio 0.18.15 and transport drones 0.1.6) i just had a crash of factorio itself when i tried to cleanup a row of provider depots and the surrounding roads. i used the deconstruction planner several times for several areas and my personal bots started the work. they first successfully removed a few empty depots and lots of roadtiles, but then factorio itself crashed with an "unexpected error". it probably happened when one bot tried to remove the roadtile under the "caution" of the non-empty depot, or when another bot tried to remove the non-empty depot itself at roughly the same time.

since i use many mods (and have many which are not yet updated to 0.18, in turn not being enabled and in turn also not included in the autosaves), I would have to install a new instance of factorio to test this again with different/less mods. this would/will take some time, but it looks as if the crash might be reproducible since it already happened twice ...