Hi, from what I see all old combustion furnace and electrolyzer entities and items got removed after the recent update. Usually I've seen mods migrating between updated entities. I don't know how easy it is to do but If it's possible it would be a nice addition allowing for seamless updates on the ongoing save.

For an ongoing save, you can enable the "1.0 Recipes" which turns on Legacy Mode; there'll be no need for migration. The overhaul removes a lot of the original content to make for a more streamlined experience. The Changelog states this and the mod urges you to read the changelog before updating. There's no need for migration because 2.0 is a complete redo of the mod's logistics.

I'm sorry, I didn't specify. Even with 1.0 Recipes enabled all combustion furnaces were removed. I'm not sure why. Maybe some legacy features weren't preserved and it was enough to not recognize the entities.

I had the same issue. Not just combustion furnaces and electrolyzer, but also D-T fusion cells and some recipes went missing. I could rebuild the buildings after re-setting the recipes, but some of the recipes are still changed or removed. At least the carbon mineralization (which seems to be a different chain now); and the Algea iron/copper combustion and Deuterium recipy seem to have changed to a different building.

I originally updated from 1.0.3, but as a test I upgraded to 1.0.7 (last pre-2.0) first (then saved, then re-enabled 2.0.1). That does not seem to make a difference; 1.0.7 gave no issues but the same things were removed moving to 1.0.7. (I did notice some recipy changes loading in to 1.0.7, but no differences in the end result).

Despite how much work I put into rhe Tritium/Deuterium chain, I completely forgot I redid their recipes to be more realistic, that's my bad. I think I can set up a migration routine for the entities. As for carbon mineralization something from 2.0 may have snuck its way in there... 2.0 a lot of 5he internals changed for Factoriopedia reasons. For now I would advise staying on 1.7 as you're not missing anything noteworthy besides the TritiumDeuterium changes. Only real reason to update is for the overhaul. (Until I get proper migrations set up)

No worries here; honestly, I was already planning on sticking to 1.0.7, or reloading a save and redo the whole thing in 2.0 (since I imagine any new changes will be for that anyway). I kind of expect a 2.0 release to break saves anyway; even a partial legacy mode is a bonus.