why does lp boost display 0% at the higher levels ?

Are you playing in a ranked flex game?

"We’re going to be launching Ranked Flex with a flat IP boost throughout the first week of the season. You’ll earn +50% extra IP in Ranked Flex between December 8 at 11:00 AEDT and December 15 at 10:59 AEDT. Whether you’re a solo warrior, a five-person clown fiesta, or anywhere in between, everyone will avail of the same IP bonus.

Oh, and by the way: due to limitations with the way IP boosts are implemented, it will appear that solo players are not included here, but this is purely a display issue - you’ll still receive the +50% extra IP at the end of the game!"

-rito