Mistico (the original Sin Cara in WWE) returned to Arena Mexico on Friday night. This is a huge story. He spoke to the crowd and talked about being born in Arena Mexico. The ring announcer announced that he would appearing at the 10/25 All Elite show. They never called him by his name and the announcers never referenced him after he appeared.
Apparently Mistico is leaving AAA soon and there appears to be bad blood with the promotion. He wrestles as Myzteziz but AAA owns the rights to that name so that is probably why he was never referenced by his name on Friday night. One rumor making the rounds in Mexico is that AAA wanted him to lose a mask vs. mask match to Rey Mysterio but he didn't want to drop the mask. He is allowed to wrestle on independent dates so that is why he was able to appear at Arena Mexico and that's why he was announced for All Elite and not CMLL since would not be able to work for them until his AAA deal is up. Arena Mexico is the home of CMLL so that's why this is such a huge story with political implications.
Mysteziz' return to Arena Mexico is similar to how he left CMLL. He never told the company that he planned on leaving and then he ended up signing with WWE. Right now the only thing known is that he is booked for the All Elite promotion and he's not signed with CMLL but this would seem to be a huge step towards a return to CMLL.
There was some heat from Alberto El Patron towards Mistico on social media back in late July. Alberto ripped on him by telling him to say things face to face instead of being a "b*tch." He added (translated from spanish), "I will break your son of a b*tch face when I see you, no balls." Alberto and Mistico have real-life heat that goes back many years.
So, Mistico leaving AAA may be the best thing for all parties.