Related to https://mods.factorio.com/mod/reverse-factory/discussion/67cec1756b0f866162e4ef87, but I thought I'd make a new thread as I don't know if it's the same mod causing the incompatibility.
https://mods.factorio.com/mod/space_age_galore and https://mods.factorio.com/mod/vanilla_galore_continued
Disabling these mods, or Reverse Factory, allows the game to finish loading.

Failed to load mods: reverse-factory/func.lua:425: attempt to concatenate a nil value
stack traceback:
reverse-factory/func.lua:425: in function 'makeFluidRecipe'
reverse-factory/func.lua:387: in function 'makeFluidItem'
reverse-factory/data-final-fixes.lua:110: in function 'final_fixes'
reverse-factory/data-final-fixes.lua:170: in main chunk

Ah, well that makes things a bit simpler.

The error is very explicitly caused by Space Age Galore, "cleaning" the ice-melting recipe by removing its order and subgroup, for some reason. I can't say I understand why, but that does make things rather annoying, since I can't rely on the ice-melting recipe to set a proper order for the fluid-melting recipes. At least now I have a point of reference to work on fixing things...

EDIT: I've asked the mod author about the issue, since I'm not entirely sure the order property needed to be removed, and any potential fix will depend on if they will update their mod to not remove the order property, since that would solve the error from their end, instead of mine.

According to the mod author on their discussion page, it seems that this issue should be resolved from their end with the next update, by removing the line of code that removes the order property for ice melting.

Regardless, the issue might crop up again with other mods if they happen to do the same thing, so I took the opportunity to fix the error from my end as well (plus an issue I hadn't noticed before, with the subgroup and sorting).

Now in the Factoripedia:

• Without Space Age, the fluid items and their conversion recipes appear in separate rows between the oil recipes and the resources.
• With Space Age, the fluid items will appear next to ice and the other resources, while the conversion recipes will appear next to the ice melting recipe and the other oil and chem lab recipes.
• With Space Age and the current version of Space Age Galore (or any other mod that removes the order from ice melting recipe), the fluid items and conversion recipes will appear in separate rows between the first and third subgroups of items/recipes (I forgot exactly what it is, but this will change soon anyways)
• With Space Age and the updated version of Space Age Galore, the fluid items should appear next to ice and the other resources, while the conversion recipes should appear next to the ice melting and other chem lab recipes, just as it should.

Either way, fixed in v9.0.22

Fantastic work Kryzeth, thank you.