On Factorio v0.17.68
Mod list:
Deadlock's Stacking Beltboxes & Compact Loaders (2.2.1)
Construction Drones (0.2.8)

I place down a chest, and put a yellow loader on it. I then use upgrade planner on the loader, a construction drone gets sent, and when it gets close enough to upgrade the loader, an unrecoverable error happens.

https://i.imgur.com/bhRmacm.png

factorio-current.log
https://pastebin.com/utW0xjZm

Update: With newest version of Construction Drones (0.2.10), an error still occurs. The error message looks slightly different this time.

Still using Deadlock's Stacking Beltboxes & Compact Loaders (2.2.1)

factorio-current.log
https://pastebin.com/r4fbxuin

Ok should be good now

Ayyyy, it works! Thanks for taking the time to fix this :D