[MC-124147] Zombie horses are invisible and replaced with regular zombies on reload

I spawned some zombie horses both using eggs and /summon, but could only see their shadows.

They move, take damage, make noise, and drop items as normal. (Their hit boxes seem about right.)

Spectral arrows do not highlight them, but they do emit particles.

They are replaced with (visible) zombies (not zombie horses) upon reload.

Game output:

Couldn't render entity
java.lang.ClassCastException: java.util.Optional cannot be cast to java.lang.Boolean
	at ait.dw(SourceFile:134)
	at bxr.a(SourceFile:24)
	at cgb.a(SourceFile:147)
	at cgg.a(SourceFile:41)
	at cgg.a(SourceFile:16)
	at cfg.a(SourceFile:362)
	at cfg.a(SourceFile:349)
	at cba.a(SourceFile:615)
	at cau.b(SourceFile:1178)
	at cau.a(SourceFile:1086)
	at cau.a(SourceFile:944)
	at bob.b(SourceFile:822)
	at bob.a(SourceFile:382)
	at net.minecraft.client.main.Main.main(SourceFile:140)

When attacking zombie horses:

Error executing task
java.util.concurrent.ExecutionException: java.lang.IllegalArgumentException: Default value cannot be lower than minimum value!
	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
	at i.a(SourceFile:147)
	at bob.b(SourceFile:782)
	at bob.a(SourceFile:382)
	at net.minecraft.client.main.Main.main(SourceFile:140)
Caused by: java.lang.IllegalArgumentException: Default value cannot be lower than minimum value!
	at abi.<init>(SourceFile:21)
	at byf.a(SourceFile:1825)
	at lf.a(SourceFile:70)
	at lf.a(SourceFile:15)
	at ic$1.run(SourceFile:13)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at i.a(SourceFile:146)
	... 3 more