I ran into a big problem when updating my world to use Unity 2019 for Quest 2: the Unity Trees straight up don't work on Quest 2. The framerate of people trying to access a world with them drops to such a low level that they have to power cycle their device. As soon as the trees are removed, the world performs completely smoothly.
Here is a link to my world that has the trees in (private test copy of the main world): https://vrchat.com/home/world/wrld_3b946fab-da19-4e60-b8c9-978c70b948d6
And here is a link to the public world where I removed the trees to prevent my Quest 2 users from suffering: https://vrchat.com/home/world/wrld_fb4edc80-6c48-43f2-9bd1-2fa9f1345621
This issue did NOT appear until I have updated the SDK (along with Unity to 2019) of my world. This is also quite a big issue, as I am assuming it will pop up on any worlds that use Unity Trees. I have tried a lot of things, but nothing worked, so the only thing left is that it is specifically a VRChat compatibility issue.