Factorio 0.18.21
Krastorio2 0.9.8
Rampant 0.18.6
RampantArsenal 0.18.8

Machine: Windows 10, Intel i5, GTX 1070

Game experiences 5 FPS and UPS. I suspect it is RampantArsenal because removing RampantArsenal causes performance to come back.

Here is the save:
https://send.firefox.com/download/b857b7ccb04d7931/#9e-JkyeCzQQpDIvdD8RzPA

Link expires after 3 downloads or 7 days

I think regen walls are the problem. They create a ridiculous number of calculations through recursion that destroy UPS . See this method here
https://github.com/veden/RampantArsenal/blob/master/control.lua#L176

In the short term, I would remove regeneration walls, and I will do so in my game. In the long term, I will see if I can find a way to improve this algorithm

Did you update to a version past 0.18.5 when this save was taken or had you been already playing on the latest version of Rampant when this happened.

I can get the save again -- it's somewhere.

Originally, we were playing on an earlier Rampant and Rampant arsenal. I updated the mods after the initial crash to see if the mods were the problem.

I most likely will need to rework the mending walls, they may end up getting replaced.

My multiplayer games always have Rampant and Rampant Arsenal, so you've definitely created a whole new type of Factorio for my friends and I to play. Thanks for that, and thanks for your hard work!

For now, we've remove the mending walls, and that's the only bugfix we need :D.