I'm using BYG as the only biome generation mod, but this issue was spotted in a vanilla plains biome on a vanilla oak tree. Problem persisted after removing Optifine. Only one side of the "fin" was white.

I'm playing on Minecraft version 1.16.4 on the Forge modloader version 35.1.13

Images of offending fin, both sides shown

Current mods:
BYG
AppleSkin
Aquaculture
Better Animal Models
Better Animals Plus
YUNG's Better Mineshafts
Brazier
Clumps
Comforts
DataFixerSlayer
Dungeon Crawl
Ensorcellation
Genetic Animals
Realistic Horse Genetics
JEI
Natures Compass
Out of Sight
Pam's Harvestcraft 2
Passive Endermen
Project MMO
Shut Up Experimental Settings
Spice of Life: Carrot Edition
Swing Through Grass
Teleporters
Upstream
Valhelsia Structures

I also jumped onto my vanilla server and the problem persisted. No optifine or mods, default launcher.

White streak in savanna oak

I don't really know how to fix this issue, minecraft is really bad at handling models larger than a block.