Okay, I need to talk about this theory or I'm going to explode.
If you noticed in tpot 20, there are certain things that are so different in XFHOV
Examples
Fourteen is hunting ZRO and not Ten like normal (besides that in the part where One was testing his powers and in the scene where Fifteen appears, WE CAN SEE ZRO INSIDE HER HOUSE IN SECONDS, 015 fans go crazy) Nine is less "fearless" or bold in tpot 20, in reality we see him crying more (in a cute way) than anything else, AND ON TOP OF THAT THE SKATE IS DIFFERENT!!
and this skate that we see in XFHOV, and the same one he created AFTER he received the powers
There are more details like we don't see the 3 in XFHOV or even 1 or 4,X for reasons I don't think I need to explain
But what about two? Most likely one didn't know that they would become depressed in a serious and worrying way, and probably took them and erased their memories and put them in this false dimension.
Now 2763... Well, probably a broken version of 3 because if we remember, its value was broken, it was cool how it appeared as a simple detail but it can change the fate of the series :D
So this place where XFHOV is, is probably a dimension created by one where everything is "perfect" that day, the day that three went to meet S*N, it never happened
Okay, now that's it: 3 blow your mind with this theory