As the title suggests, 1.12 is crashing with pretty much all mods, let me list a few:
Quark, Simple teleporters, Iron Chest and RFTools. (Possibly more, haven't tried that many mods)
Even though they are supposed to be up to date(hence the speak marks under "compatible")
You can try these mods for yourself and see if they crash you.
Here's the crash report for when I tried loading Quark(And some other mods): crash-2017-07-06_20.52.26-client.txt
This is the error I'm getting 99.9% of the time: http://prntscr.com/fsijeu
"It looks like you're using an unsupported modified version of the game" is the error.
I really hope somebody can help me, thanks in advance.
Regards,
-L0ST