The description for the heat exchanger states that it converts water into hot steam, as per un-modded Factorio. However the prototype actually wants steam as input instead like the mod-specific "heat changer". I do not know if the behaviour is intended and the documentation wrong or vice-versa, but either way the contradiction seems like a bug.

Here is another bug as a side note: assemblers and chemical plants in "attract" mode do not seem to work, presumably because the selected vanilla recipes do not exist. Custom screens would look cool, though I understand that that might not be worth your time.

Another weird bug(?): for some reason, I can get digit 2 as a logistic request, but not 3, 5 and 8. I have not set up any addition recipe yet, but it seems that 0, 1, 4, 6, 7 and 9 cannot be selected either.

The heat exchanged bug should be fixed in version 1.2.1. Thanks for bringing to my attention ^w^
As for the logistic request bug.... I genuinely do not know what the problem is. I was able to reprodeuce it, and spent like 30 minutes trying to track down what's going wrong to no avail. That'll be a project for another day when I have more time >w<

Thanks for the fix!

Regarding the digits, the issue is much broader: they can't be selected for inserter filtering and in circuit logic either. FWIW, the game seem to treat them as "unresearched" (according to Recipe Book), except for "2". So seems that 2 gets some special handling that 3, 5 and 8 don't..

I think factorio considers the item as researched when you research a recipe that can either use or produce it. You get the 2 early because you can get it by decompiling a Z; you don't get the 3/5/8 until you research the necessary uranium sciences.

Ah, that explains why 2 works. Though I have fuel reprocessing though. 3, 5 and 8 are recipe (decompilation) produces of the isotopes, which are produces of the depleted fuel. I even have Kovarex so I think I'm done with nuclear techs.

I suppose they are incorrectly gated by the addition tech. I'll see when I get there.

Other numbers unlock with the addition tech. I guess it's caused by decompilation recipes having the unlock flag set to false. But maybe there's a reason why it's needed

Yes, I think that's it. https://codeberg.org/FoxSylv/Verbose-Engineering/src/branch/main/utilities/createDecompilationRecipes.lua#L31 sets unlock_results=false for most decompilation recipes, which means that unlocking uranium decompiling does not unlock the 2,3,5,8 digits.

The letter decompilation recipes do set unlock_results=true (which is default), and each letter can decompile to itself, so all letters are unlocked items as soon as you research letter decompiling, as well as 2 from decompiling Z. But unlocking uranium-238 decompiling does not unlock 3,8; digits only get unlocked once you have a non-decompilation recipe that produces them, such as number addition.

I don't see any reason why decompiling should use unlock_results=false; removing that should fix the problem for 3,5,8. It does get the slightly weird situation that unlocking uranium processing unlocks 3,5,8 but not the other digits, but that shouldn't be a real problem (you legitimately cannot reach the other numbers yet at this point); it's just a UI peculiarity.

This issue should be fixed in Version 1.3.0 ^w^