I loaded a Realms Plus template and dit a fly around the island and found a broken jungle leaf texture. I mined one of the leaf blocks and found it produced jungle leaf particles and unsuccessfully tried to fix it using a light source (it usually works). Another thing I found was that it was not under a light-obscuring block as I have found where the most lighting issues occur.

The template was a world created in the Village & Pillage update and had mods.

Years ago, I came across a similar issue except it was in a Vanilla world.