Just played a game as Riven who I have level 6 on. I earned an S rating on her but didn't get the token for it. I checked the hextech crafting tab if it was there and it wasn't. Am I not supposed to earn them in these game modes or is this a bug? My friend told me they earned a token when URF was out.
i didnt get one for poro, special modes seem to have tokens disabled, not sure if riot ever mentioned it.
Mastery tokens currently are only given out when playing on SR.
http://na.leagueoflegends.com/en/news/community/q/chromas-yorick-and-champ-mastery-ask-riot
As some of you have pointed out, mastery level 1 to 5 are as much about continued play on a champ as they are about skill mastery, great play just accelerates gains. Mastery level 6 and 7 have a higher competitive bar as far as performance requirements. Alternate game modes are intended to offer variety in play with a less competitive standard for players. We want to maintain mastery levels 6 and 7 as achievements specific to high performance in competition, so they will only be achievable in SR modes. - Riot Socrates
I'm pretty sure that mastery tokens are disabled for RGM matches
