I've tried using iron plate as per JEI from every mod that lists an iron plate and without success, this essentially breaks the fundamental requirement to start IC2 since a good amount of its machiens require the machine casing.

I'll look into it but for the meantime can you see if you can make a TechReborn basic frame and then craft/convert into an IC2 frame in crafting grid?

Del and reapply of fresh scripts folder indeed solved the issue

A user on discord reported similar issues with recipes. They were using CreeperHost's server update not setting up files manually. After downloading a fresh profile and deleting and then copying over fresh scripts folder the issue was fixed for them. Can you confirm same steps? Manually/FTP delete then re-upload scripts folder from fresh client profile/download and report back?