Riot just realized Unflinching was bugged all the time since it exists
http://www.surrenderat20.net/p/current-pbe-balance-changes.html#balance
Unflinching (R4) [Bugfix] Now properly grants 10% slow resistance for each summoner spell on CD
Yesterday the buff was 18% Tenacity instead of 15% And while buffing it they realized it was never working like intended, lol.