Reported on arachnids because i believe they are the culpit, but maybe this can or should be fixed on this end. See other thread for details.

https://mods.factorio.com/mod/Arachnids_enemy/discussion/656b75cf6a11d39b25d5db47

Unfortunately, there is not enough information. If I understand correctly, then you (or mod) removed the "Arachnids" faction from the list in the editor (for example) ?

A save is most likely not needed, since the cause of the error is some sequence of actions leading to an unexpected situation
It is necessary to describe the steps for reproducing the error and the set of mods.

Involved mods are rampant fixed, and both of those

https://mods.factorio.com/mod/ArachnidsFaction
https://mods.factorio.com/mod/Arachnids_enemy

I also have explosive biters, frost biters, armoured biters, on a full SE+K2+248K+BZ megapack, but the rest is most likely unrelated. I can provide a full modlist if needed.

The game crashes when starting a new game (see other thread for error) so there is no save to be provided anyways.

I'm now unsure if rampant detects the arachnids mod (despite not being the regular one that is marked in the dependencies) and then fails when arachnids on biters removes the faction or if it's arachnids on biters which fails removing the new faction and rampant gets confused.

I would like to use them over the regular arachnids because they are better maintained and come with a range of improvements over the original. I have not tested the regular arachnids to see if it replaces the default biters if they are left enabled in rampant but that isn't something i want either.

Think I understand how this could happen.
ArachnidsFaction added a faction and notified about it.
Arachnids_enemy deleted faction and did not notify about it and my mod is trying to process it.
I think that's enough. I will put additional checks

Now version 1.8.0 is in semi-finished form, but I can’t say exactly when it will be ready. Approximately at the end of December

Thanks

Unfortunately, I forgot about this in the 1.8.0 release...
I'll try not to forget for the next one

Hello, it seems the fix has not been introduced yet. Is it still planned?

It's good that you reminded
I forgot about it
Version 1.9.0 is being slowly made, I will add this fix in it

hopefully soon then cuz im having the same issue xD

It looks like combination of these mods is being used more than I thought.
Okay, I'll make an intermediate version with a fix for this
Estimated - in 2-4 days