My game crashes under this cirumstances:
I have two Spidertrons following me (a vanilla one and a Cannon Spidertron), then I die and hit 'Respawn'. When one of the Spidertrons get destroyed during this time (it was the vanilla one), the game crashes with this message:

The mod Spidertron squad control (0.3.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Spider_Control::on_nth_tick(20)
Spider_Control/control.lua:63: attempt to index field '?' (a nil value)
stack traceback:
Spider_Control/control.lua:63: in function 'validate_spiders'
Spider_Control/control.lua:76: in function 'spiderbot_designate'
Spider_Control/control.lua:295: in function <Spider_Control/control.lua:284>

The game does not crash, when only one is following me and dies, no matter which one.

I am playing a scenario with a lot of additional mods installed. The Respawn time is set to a minute (at least it should be). There are other bugs in this save that I am aware of, but they should not interfere with the spidertrons (the GUI of the scenario and Robot Recall).

Here is my save for testing purposes: https://drive.google.com/file/d/1yUlQADt5x-SSjHaIwN3ELpDPTTdr7MFC/view?usp=sharing

im not sure what is causing this, tried reproducing it in 0.3.2 (next release) but could not find anything. if you still get the error in the next release let me know

I tried again with 0.3.1, and it doesn't happen anymore. Maybe my game just needed a restart?
Let's consider this a wrong alarm / solved for now. Sorry for the inconvenience.