I'd say it's most likely one of four things:
1) Have you ever been on, or are you currently on SSRIs or a similar form of medication? These interfere with Serotonin receptors somewhat long-term and reduce the effects of Psychedelics and various other drugs that influence Serotonin. It's normal for someone on SSRIs or who used them for a long period of time to need 2-4x the regular dose of psychedelics for similar effects.
2) The quality of the 2C-E is not up to scratch. By the vastly differing dosages people mention I suspect it is likely that there is a lot of low quality 2C-E around, this sort of makes sense given that it is very potent and most people won't notice an impure/cut product unless they've taken a more potent one in the past. Even if it is the most reliable dealer/vendor you've ever used, never be afraid to question the quality - people make mistakes.
3) Tolerance or cross-tolerance. Although your second trip was after a week break, which should be good, you should give it two weeks without consuming any psychedelics, the fact is you only mentioned research chemicals for one - and any psychedelic that affects 5ht2a receptors has cross-tolerance with other psychedelics that exert the same effect. However, even if you didn't take *any* drugs whatsoever in that week, still try two weeks, you said that prior to your first trip you tripped twice in two days, so that could easily significantly increase your tolerance, and it might take longer than usual to hit low/baseline tolerance.
4) Eyeballing. I'm only adding this one in because of personal experience. 20mg looks like 10mg looks like 40mg looks like 60mg - the human eye isn't good enough to accurately measure out such a small dose of a fine powder. I'm sure you're most likely not eyeballing, but if you are, as I have done, then it's easy to think you're taking a much smaller/larger dose than you actually are, so your 60mg dose could be as little as say 15mg. If you are eyeballing, get a scale.
Hope this helps. Of course it could be something else, and some people just act unnaturally to certain drugs.