GPU: GeForce GTX 1080
CPU: Intel i7-8750H
RAM: 32GB of DDR4 at 2400MHZ (Allocated 2, 4, 6, 8, 10, and 12GB respectively for testing purposes)
JAVA VERSION: 1.8.0_201
OS: Windows 10 Pro (Build 17134.556)
When a tree is burning, the burning of the leaves causes unbearable lag, causing my computer to drop to 10FPS, though if I leave the chunk the tree is burning in, the lag subsides.
Best of luck.
EDIT: I have found out that the cause of the lag is the breaking of the leaves from the tree. All animations that happen quickly and in quick succession (such as breaking leaves, water flow, many entities, cause huge stuttering lag. This is with most of the animations in this current patch.
Here is a video of it I made --> https://youtu.be/lC7PM9dRWLg