Lately in a game I started recently, while the FPS/UPS is normally great most of the time, but sometimes it will "stutter" for 5~20 seconds, with terrible lag spikes where the screen looks frozen for 1~2 seconds at a time. These stutters seem to get even worse while either biters are attacking, or I'm near my defense walls. I used the debug (F4) screen to show the use time, and it seems whenever these lag spikes occur, the usage for RampantFixed goes up very high, so I think it may be related.

This game has been going for about 45 hours, and uses Krastorio 2, RampantFixed, and a few simple QoL mods like Helmod, FNEI, etc.

Any ideas on things that could be causing this / things I could do to help? I've already disabled the Biter Blood animations, and also lowered the Difficulty & Temperament settings to 0.25 since I was totally unable to keep up the Rampant enemies using essentially vanilla weapons / defenses (I'm a long ways from unlocking any of the powerful Krastorio 2 weapons / turrets).

Here is my save file in case it could be checked. For an example, upon loading the save shoot the nearby nests to the west with the sniper rifle, and notice the spikes of lag / stuttering / freezing.
Save file: https://file.io/FmIdqGY9gxAy

(Also, unrelated question: Is there a way to change the behavior of the AI in Rampant, fixed so that when I attack a biter / nest / hive, it only causes biters in that area / region to become aggressive and attack, instead of making all biters everywhere on the map all start attacking all parts of my base at once anytime I attack any biters?)

Thank you for the save. The problem is reproduced. It will take some time to find the cause.

How will I deal with this, I will answer other question. Preliminary answer - the destruction of nests gives Rampants (both) points for active counteraction. In addition to sending "revenge squads", these points are spent on "current needs". I'm not sure it's worth changing this, because it dramatically reduces the danger of enemies. But, perhaps, it is worth applying the difficulty coefficient to the points received for the destruction of nests

Thank you very much for the prompt reply!

I should add in case it is relevant, that I originally started the game with different settings for Rampant, fixed and for the base game enemy map settings, but have been reducing them back towards default settings as I’ve found things more difficult than I expected.
E.g. for Rampant, fixed I started with all new factions enabled, migration enabled, etc. and I started the map settings with enemy nest frequency & size at 200% &150%, and the various evolution factors at default.

That explanation for the second question make sense, thanks.

Interestingly, I discovered something related to it last night, which has been helpful for me:

I found that when I attack nests using the tank instead of on foot, only the nearby nests in the area counter-attack, and they become calm again much faster than if I attack on foot with the sniper rifle / rockets etc.

This method is still quite challenging (taken me an hour or more just to clear 1~2 dozen nests near the uranium patch) but makes it more possible to claim a little territory.

1. The main reason for the lags is a lot of active chunks with 500+ nests and worms in each (!!) next to the player. This is more typical for the standard rampant and fixed versions before 1.0.16, when hives produced worms and nests endlessly. This removed the performance margin the game, even with the scripts turned off, runs at a maximum speed of 1.5x
2. The second reason is when all these 500+ objects in the chunk are trying to mutate. In addition, when the map is overpopulated, even the slightest changes in genes lead to the verification of mutations.
   It is also the answer to why military actions cause such a strong response

Work is underway on a solution:
According to the situation with mass mutations, a "queue" will be introduced in the next version to distribute the load.
To solve the problem of overpopulation, the probability of the death of nests/worms will be added if there are too many of them.
Code sections have been found that do not cause serious lags, but are quite resource-intensive with a huge cluster of nests

I guess it will take a 3-6 days (edit: 1-2 days)

Wow, thank you for the detailed explanation! That all makes a lot of sense, and thank you for looking for a solution.

Haha, I was actually also quite surprised at how many nests / worms were growing near my base, and it was much more than I expected or planned for! It had been a few years since I last played Factorio / Rampant, and I couldn't remember what sort of settings I used for enemies so I just guessed. I ended up with way more nests / worms than I wanted, and apparently too many for me to handle (I've already technically "lost" this game since I had to cheat earlier to give myself some iron, since I quickly ran out before I could clear enough nests to reach the next iron patch. However I'm still having fun working my way through this save file despite it).

For future games I may start, are there any tips on which settings for Rampant, fixed, or enemy map settings I should use to get fewer nests and worms starting out? Clearly starting the game with enemy nest frequency at 200% and size at 150% was a big mistake for me until I reduced them back to defaults!

1.0.18 released.
Since overpopulation control has been introduced, I recommend postponing attacks for 5-10 minutes until the number of enemies decreases naturally.
However, there should be no lags right now.

For the future games , it should be understood that in the "fixed" version, "migration" = "survival mode against endless sieges".
New factions are able (and will) to mutate from existing nests and do not require space, unlike a standard Rampant. The first mutations are possible from 15%

For those who want a serious test, the standard deathworld with default Rampant Fixed settings is more than enough. Moreover,I usually increase the wealth of iron - otherwise you may not have time to occupy a new deposit.
For an interesting game, with a real risk of losing in the absence of proper attention to the map - even a standard world will do. On it, the player will have about 1.5-2 hours before the world accumulates enough strength for dangerous actions.

The basis of a successful game against this variation of rampant - is map control. At the beginning of the game, the mod only distracts attacks from the main danger - the appearance of inconspicuous nests in the most unpleasant places. If you skip them, then the world itself will take care of the player.

Biters have protection from cheat protection systems, like bob plasma, snipe turrets, so that Biters able to resist it with standard health - it can be left by default. The factions are balanced so that their features are opposed to different defense systems. Example: If you'll check fast biters resists - you will see that they cannot be killed with a sniper rifle.
The most interesting game will be if every faction is present - you will need to design a universal defense. But in the current game, this is definitely not worth doing )

Thank you so much for the fast update! Right away I could see the amount of nests / worms reducing to more normal levels, and haven't had any lag spikes since updating, it's perfect!

Thanks also for the explanation of settings; Looks like I really had the settings turned up more difficult than I thought, especially with Resource Spawner Overhaul making Iron / Resource patches farther away.

I'm excited to continue this save now, while returning more settings back to their default values (though I will keep many of the elemental / dangerous new enemy factions disabled for this save probably).

Thanks again!