After updating from 1.0.7 to 1.0.8, I have lost the ability to use the void flux and coherence variants of the recipes. Their tabs no longer appear in the voidworks, existing voidworks show that the "recipe [is] not researched", but Factoriopedia does not list a research for them.

Well, I don't know what went wrong... but I do know how to fix it!

I added a console command to 1.0.9, /vc_fix_recipes and the recipes should come back.

It's so weird that there's still no native way to have a recipe require multiple prerequisites.

So that worked, and I can tell you what went wrong, because I can replicate it.
"The game resets recipes and technologies any time mods, prototypes, or startup settings change"

Since you're unlocking them programmatically, there's no technology unlocking them, and so they're getting reset to locked. Any, and every, time any of those things happen. Add a mod to the save? Gone. Remove a mod from the save? Gone. Change a startup setting? Gone.
Unfortunately, I don't have a good solution to offer you outside of having that command available.

There actually is supposed to be a solution, an event called on_configuration_changed, that is specifically designed to handle this very situation, and Voidcraft makes use of it. I instantly knew how to fix your problem because I got bit by the same thing early in development, when I was constantly adding new features, and that's when I learned about on_configuration_changed and added it to the mod. So the mystifying part to me is that something in the configuration changed that didn't cause on_configuration_changed to get called. Possibly a bug in Factorio itself, but I don't think we have enough information to write a useful bug report.

Ah, that's good info -- another mod I have is calling reset_technology_effects() when that event fires, which is.. totally overriding you. I'll file a bug report with them, because that's entirely redundant in the first place, but I guess you could also solve it on your end by also handling on_technology_effects_reset.

EDIT: Hmm, removing the mod in question didn't fix it, but, indeed, adding this handler did.

script.on_event(defines.events.on_technology_effects_reset, force_unlock_variants)

I guess there's multiple mods doing the same pointless thing.

Thanks, I've added this to the next version.