Okay, 1.12 isn't working for me (on the technical side). It went fine for an hour or two but now I can neither load my world nor create a new one. That will probably have to wait until I get a better PC then. Back to 1.7.10. That's a bit sad because I was getting somewhat hyped for astral sorcery and some of the new mod features (as well as the new building blocks).
Edit: I don't really know what to put in my town hall, what did you add to yours?
@5argan, I've found that with 1.12, unless you have a PC with a smallish amount of RAM or a rather old CPU, 1.12 actually is pretty stable. Not that I am against 1.7.10, as that is what I have reverted to for now on my own games right now, but from my experience everything from 1.10.2 onward is usually a lot easier on your computer than equivalent 1.7.10 packs. Do you have a system that is running on 4mb of RAM or less? Have you specifically remembered to allocate more than the default amount of RAM to your modpack?
One thing my daughter (who also plays on my pack from time to time) often forgets to do is reset the RAM allocated to minecraft when she downloads a new iteration of the game. The twitch/curse launcher isn't usually too bad about this once you've configured it and told it to allocate more RAM, but MultiMC in particular has a bad habit of resetting the RAM allocated to minecraft back down to 1GB every single time she reinstalls the pack.
When she forgets, the pack either never loads (no crash, it just eternally hangs) or it crashes at some point during the load. Rarely, it actually loads anyway, but her FPS drops into an unplayable single-digit range. At that point she remembers that she probably forgot to reset her RAM allocation, quickly bumps it back up to something reasonable, and the game works fine with no lag or problems.
For reference, my (senior) mom also plays on my server, and she does fine on a system with 8GB RAM, allocating 4GB to the pack. My daughter has a 32GB system, also allocating only 4GB to play smoothly. I run a 64GB system, and on the rare cases when I forget to bump up the allocation to 4GB, it will fail miserably. Just giving the pack enough room to breathe at 4GB is usually more than enough for all but the largest kitchen-sink pack I've ever put together.
Your mileage may vary of course, but this (apart from derpy config conflicts between mods back in 1.7.10) is 90%+ of the problem I've experienced when putting things together in packs for this challenge.