Entering certain chunks causes instant "exception ticking world" crashes. Seemingly related to leaves - as I was flying around, I would notice random leaf breaking particles appearing on the edge of my render distance when a chunk that were being reloaded. Crashes happened in areas with dense foliage, test cases reported below:

-Player who tried spawning into a jungle would instantly cause server to crash (render distance 10)
-Player flying towards a normal forest would crash the server (render distance 10)
-Regular forests and the edge of jungle was fine at render distance 4, but going into the jungle would cause immense lag for the client (60+% CPU usage in the client alone for my machine mentioned above) and had high likelihood of crash.
-Even when I didn't see the particles upon chunk loading, I noticed many natural trees I wandered into had obvious missing leaves, but no new decay would occur.

Map was created in an earlier snapshot and upgraded directly from 18w21b to 1.13 pre-1.

It seems to me as though it's an issue with chunk loading where every leaf block does a decay check upon the initial load.

Server log and associated crash report below, all other tests had exact same crash report.

[13:33:38] [Server thread/ERROR]: Encountered an unexpected exception
h: Exception ticking world
	at net.minecraft.server.MinecraftServer.w(SourceFile:697) ~[113.jar:?]
	at rx.w(SourceFile:365) ~[113.jar:?]
	at net.minecraft.server.MinecraftServer.v(SourceFile:626) ~[113.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:531) [113.jar:?]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_161]
Caused by: java.lang.StackOverflowError
	at bog.f(SourceFile:85) ~[113.jar:?]
	at bqm.a(SourceFile:46) ~[113.jar:?]
	at bql.a(SourceFile:445) ~[113.jar:?]
	at bbi.a(SourceFile:270) ~[113.jar:?]
	at bfx.a(SourceFile:225) ~[113.jar:?]
	at bfx.a(SourceFile:195) ~[113.jar:?]
	at bog.a(SourceFile:209) ~[113.jar:?]
	at bbi.a(SourceFile:304) ~[113.jar:?]
	at bfx.a(SourceFile:225) ~[113.jar:?]
	at bfx.a(SourceFile:195) ~[113.jar:?]
	at bog.a(SourceFile:209) ~[113.jar:?]
	at bbi.a(SourceFile:304) ~[113.jar:?]
	at bfx.a(SourceFile:225) ~[113.jar:?]
	at bfx.a(SourceFile:195) ~[113.jar:?]
	at bog.a(SourceFile:209) ~[113.jar:?]