I've searched large portions of many worlds in creative generated after 0.17 and have found no lapis ore in any of them. I've checked in extreme hills, plains, and most forest biomes.
MCPE-18465
Lapis lazuli not generating naturally
Resolved
Cannot Reproduce
0
(Unassigned)
Unconfirmed
Tablet - Android - Lenovo A10
Android 5.0.1
0.17.0.1
Retrieved
You reproduce the issue by creating a new world in 0.17.