I have linked my Battle net ID to my Twitch ID and watched at least 30 full games with my Android phone, but now, I just have 24 tokens. Why?
You get three tokens for every live match you watch.
(I guess you watched a bunch of older matches)
By the way,
after the final map of a match, a random number of viewers will get 100 League tokens, so keep an eye out for that.