As the title suggest, i was able to reproduce consistently the error shown here :
https://ibb.co/kKnc3fW
It happened in a game that has Nullius mods and other mods too, so i made this save game in case :
https://easyupload.io/kzezn9
I known it says 1.2.0 on the screenshot, but when typing this message i realized you updated the mod some hours ago, so i tried with 1.2.1, on a non-modded map ( with just Renai Transportation) And the same thing occured :
Step to reproduce :
Use the hotkey CTRL+X in order to "cut" the inserter located on the right of the player.
if you don't press any key, you now have a green preview of the inserter following the cursor, as for "paste".In this particular stage, pressing F will cause the error.
And also , if you just do CTRL+X, and then clear cursor, do other thing then CTRL+V and it is the thrower inserter that is ready to be pasted . Then pressing F as to change the throw distance of the green preview, will cause the error.
To make the mall on the left side i tried to place the throwers with their range already set. Some time i missclick and boom :/. My other way to do is using picker dollies mod, to move the thrower after i set their range, to try and reduce the spill over but it's not always possible x)
Still a super fun mod i recommend !!!