I got the following error out of the blue:

The mod Renai Transportation (1.2.8) caused a non-recoverable error.
Please report this error to the mod authoer.

Error while running event RenaiTransportation::on_script_trigger_effect (ID 155)
LuaItemStack API call when LuaItemStack was invalid for read.
stack traceback:
[C]: in function 'index'
__RenaiTransportation/script/event/effect_triggerd.lua:79: in function<RenaiTransportation/script/event/effect_triggered.lua:8>

I've been running the mod for quite some time now and this is the first time this popped up

That's weird, it looks like the item in a Primer Thrower somehow disappears while the thrower tries to throw it. Not sure how that happens but its simple enough to add a check for it that should(?) prevent the crash