Just picked up a crash. Will update with more info as it arises.

The mod Ghost Scanner 4 (4.0.4) caused a non-recoverable error.. In editor
Please report this error to the mod author.

Error while running event GhostScanner4::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__GhostScanner4/control.lua:393: in function 'UpdateSensor'
GhostScanner4/control.lua:450: in function <GhostScanner4/control.lua:441>

Update: I loaded a previous save and a few seconds after I cut the ghost scanner along with some combinators to move them I got the same error.

Hmm, I bet the editor doesn't call the expected created/destroyed events when messing with entities.

I'm unfamiliar with the editor, could you give me step by step instructions on how you're performing a "cut"?

I use ctrl-x and drag a selection box over the desired items to cut.

I got an error in the editor extensions editor mode as well when doing a cut over a ghost scanner

The mod Ghost Scanner 4 (4.0.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event GhostScanner4::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__GhostScanner4/control.lua:394: in function 'UpdateSensor'
GhostScanner4/control.lua:451: in function <GhostScanner4/control.lua:442>

This also happens when using the sandbox mod, which is area in editor mode for making blueprints. so not much difference, but wanted to point this out.

it also happens when resetting the 'world' in sandbox too, which means that it cannot be removed once placed!

I really liked this mod, but the same error also occurs when I delete or cut

This bug still happens. A pity that the author does not bother to fix it.

This is how you can fix it yourself: edit control.lua. Around line 451 UpdateSensor is called where the error happens.
The original line looks like this:

UpdateSensor(storage.ghostScanners[storage.updateIndex + 1])

Replace the line with these two lines:

local ghostScanner = storage.ghostScanners[storage.updateIndex + 1]
if ghostScanner.entity.valid then UpdateSensor(ghostScanner) end

I cannot guarantee that my patch is side-effect free but at least it does not crash any longer.