[2.1.9] Crash placing space platform tiles, UndergroundBelt check fails

[Kibb99]

Likely caused (or at least partially caused) by the mod Staged Blueprint Planning https://mods.factorio.com/mod/bp100

factorio-previous.log

(22.8 KiB) Downloaded 17 times

Using the stages, some buildings were placed with no platform underneath and holes that wouldn't normally be possible.
I was placing platforms to make it valid (roughly 10x10 size, dragging with WASD) and the game suddenly crashed (I think when i got a delivery of space platforms and it tried to start expanding the platform like it normally would)

All Mods:
Elevated Rails, Quality, Recycler, Space Age, Assembly Analyst, Cursor Enhancements, Editor Extensions, Factorio Library, Factory planner, Far Reach, Rate calculator, Sandbox, Staged Blueprint Planning

[Kibb99]

To reproduce, place tiles under the left side like I described first, then when enough tiles get delivered it will crash

_autosave1.zip

(3.03 MiB) Downloaded 21 times

[Genhis]

Thanks for the report. I can't reproduce the crash from your autosave. Could you post a video?