That sounds like you haven’t been paying attention to what has been going on. There have been several occasions where mythic troops were entirely missing from chests. Here is one them:
Note that this particular incident happened several weeks in a row and also got stonewalled at first. Once enough irrefutable proof was presented the very latest incident got compensated. The one a week earlier that kicked this off? Oops, we lost the logs needed to compensate this while waiting for it to play out, totally by accident. But trust us, there really wouldn’t have been anything to see in there, here’s a wall of text with a lot of dodging to explain why.
There has also been at least one issue where the chance for legendary and mythic troops from event chests was proven to be significantly reduced, to roughly half the stated odds. This usually takes a lot of data analysis to detect, so it might actually happen quite more regularly. For this particular case, their support also refused to refund, claiming that a rollback would “cause players to lose all the shiny [low rarity] troops they received, so it wouldn’t be in their best interest”.
As for not getting the mythic you like, it’s quite difficult to actually get the one you like when it has secretly been removed. Note that the exclusivity for Archproxy Yvendra was officially announced to not apply to event chests, Infinity Plus Two is deliberately trying to make this appear not exclusively their fault. The event post got edited a day after the incident, the information about Yvendra wasn’t there at first.
