Edits to mastery page in champ select aren't saved [Client]

I built a new mastery page during champ select (solo queue), but once i entered the game the page was blank (checked through lolnexus and had no keystone mastery in game).

Once the game ended I checked, and the mastery page appears blank (in my summoner profile).

To reproduce the bug:

1. Enter champ select (Bug wasn't reproduced in custom games, only in solo queue).
2. Open a new mastery page and select it as the active mastery page (I only tried new pages, but it is possible that editing old ones won't work either).
3. Enter the game (mastery page should be blank).

This happened two games in a row (haven't tried it again because I'm not too keen on playing without masteries).

Thanks