As of version 1.16.4-2.0.1, when a tree in this mod is generated, all leaves have their DISTANCE property set to 1. The distances only corrects themselves when a nearby leaves block is broken.

Looks like your MapleTreeFeature class is extending directly from Feature<BaseTreeFeatureConfig>:

Minecraft's net.minecraft.world.gen.feature.TreeFeature already handles updating leaves distances at generation time, so y'all might consider extending that class instead? Biomes O Plenty uses it pretty painlessly* (see https://github.com/Glitchfiend/BiomesOPlenty/blob/02157af333cf7b917746cc6e6d966fc58a2b67f5/src/main/java/biomesoplenty/common/world/gen/feature/tree/TreeFeatureBase.java#L191; if the changedLogs and changedLeaves sets are populated with the generated logs and leaves blocks, then leaves distances will automatically be updated by TreeFeature code).

Edit: *BOP makes it look easy by using custom mappings and forcing functions to be public... maybe the TreeFeature class comes with too much baggage, but at least it's something to reference

Why I care -- my TreeChop mod uses the leaves DISTANCE property to decide which tree each leaves block belongs to. The mod allows a whole tree to be broken at once, also breaking any leaves that "belong" to it. When two Autumnity trees are next to each other but their leaves have the wrong distance values, I can't tell which leaves belong to which tree.

I know it's a tiny, tiny thing, but fixing this would be very much appreciated.

Fixed in 1.18+

Thanks!