So it looks like the last patch broke the current ICC (and probably all old content) skip.
Working on trying to figure out how to do it. After the prepatch on Tuesday it still worked fine so it must have been yesterday or the day before that it was broken. Will never understand why they added a skip to some old raids but not others. such a pain.
I’m currently trying to test old methods, if anyone figures out a solution so we can add that as an update to guides that would be lovely.
Edit for clarity and transparency:
What is happening now is that following the previous steps (have 10N lockout with the booster, solo kill boss on 25H then join the booster’s group, kick the leader after accepting the lockout, kill 1 extra boss, run out, reset and then go kill arthas) now result in the following:
Upon leaving the raid to re-enter and kill Arthas you are told you are locked into a different difficulty. We tried twice, and it always ends with the person being skipped ending with a N25 lockout, not H25.