I don’t know what is going on to cause this superman feeling right before the wheels come off. I’ve studied OTS for decades and have yet to find anyone that can explain all the causes. Most of what I (and anyone who has studied it) can offer is observations of typical signs and symptoms.
It’s just a guess based on seeing this play out many times but….my guess is that you feel like superman right before disaster strikes because you are at a new level of fitness and performance potential. The temptation is to pile on more training because of what you were doing got you this fit then surely doing more of it will make you even fitter, right? I don’t think so. In this situation your body is in a place it has never been (or at least for along time) in terms of performance potential. That is why I recommend dropping back in training load when you see this begin to happen.
Your improving interval times with a drop in RPE seems totally consistent with what I have said above and talked about in the OTS podcasts with Phil and the other with Sam. It does not need to be improved maximal performance.
I’m afraid this is the best I can do in terms of an ‘explanation.’