This is relevant to the Blueprint Sandboxes mod (https://mods.factorio.com/mod/blueprint-sandboxes)

Steps to reproduce:
1) Blueprint Sandboxes >= 1.6.0
1) Place a searchlight inside a blueprint sandbox surface
2) Clear the surface without removing the searchlight manually

I've encountered a similar problem before with the Stack Combinators mod, relevant thread:
https://mods.factorio.com/mod/blueprint-sandboxes/discussion/625a411f1e0ae975b98973a1

Error text:

The mod ⚠️ SearchlightAssault ⚠️ (2.1.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event SearchlightAssault::on_entity_destroyed (ID 158)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__SearchlightAssault/control-tunion.lua:472: in function 'GestaltRemoved'
SearchlightAssault/control-gestalt.lua:464: in function 'SearchlightRemoved'
SearchlightAssault/control.lua:467: in function <SearchlightAssault/control.lua:465>

Thanks for your report, I should be able to put out a fix soon.

I have released version 2.1.2 which should fix this issue.

I wasn't able to replicate the issue with your steps here, but trying to cause it with the save-load cycling you mentioned in the other thread did.
This behavior is very strange, so if you see any further problems please let me know.

The new version should start to appear in the mod portal shortly.
If you don't see it in-game you can download it manually here: https://mods.factorio.com/mod/SearchlightAssault/downloads

Thank you for your work, it's much appreciated.