Its been noticed in the last update enter triggers haven't been working correctly. its been hard to narrow down everything but i have been able to find some. example world here:

( https://vrchat.com/home/world/wrld_4d2993b2-9c91-4e10-bea1-31a424e43659 ).

everything works fine in 2017.

in 2018 if you have a nontrigger collider on a gameobject enter trigger isn't firing, but trigger colliders are working fine with enter trigger.

if you have multiple colliders on one gameobject it can also not work. if you have a standard collider above the trigger collider in the component list nothing happens. but if the trigger collider is above the standard collider it works fine.