SLA prints not sticking to build plate
Prints could end up on tray for couple of reasons. 


Vacuum force on early layers - Usually you should lose pieces on the center of platform


Put holes or channels on platform
Very slow speed on early layers
Use smaller platform
Use tilt mechanism
Use larger support structures
Use stickier platform - Anodized aluminum is specially good 

Non-aligned platform - Pieces on side of platform end up on tray 


Align platform / tray

Low cure times - you could lose pieces around platform for DLP and whole platform for LCD ones
Resin related issues


Resin designed for thinner layers - Decrease layer thickness
Pigment settled down - Shake resin before use