Crashlog (Pastebin): https://pastebin.com/ieg5ihVL
Minecraft version: 1.12.2
Forge version: 14.23.4.2738
Exchangers version: 2.7.3

That happened when I switched to easy recipes mode. It seems like you haven't specified the key "O" for the easy EnderIO Darksteel exchanger recipe.
The mod is cool, keep working on it!

Will be fixed on 2.8, recipes are being rewritten for 1.12 EIO as well.

OK, I'll be waiting for it. Thanks for help!

Keeping the issue opened until it's fixed, so I can keep track on things.

OK

Sorry for the delay on the update as I've been extremely busy, but this is finally fixed in 2.8!