Crash when loading some worlds: IllegalStateException: Lock is no longer valid

In the Experimental Settings load menu, if I click 'Backup & load', I crash with this error:

Test world

Stack trace

1.16-pre1\: [^crash-2020-06-04_15.03.48-client.txt]

Description: mouseClicked event handler

java.lang.IllegalStateException: Lock is no longer valid
	at daa$a.i(SourceFile:297)
	at daa$a.h(SourceFile:431)
	at dtv.a(SourceFile:176)
	at dlt.a(SourceFile:1850)
	at dph.c(SourceFile:42)
	at dne.b(SourceFile:33)
	at dmy.a(SourceFile:16)
	at dnc.a(SourceFile:149)
	at doa.a(SourceFile:27)
	at dlu.b(SourceFile:92)
	at dqn.a(SourceFile:431)
	at dlu.a(SourceFile:92)
	at dlu.c(SourceFile:162)
	at amk.execute(SourceFile:94)
	at dlu.b(SourceFile:162)
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36)
	at org.lwjgl.system.JNI.invokeV(Native Method)
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3050)
	at com.mojang.blaze3d.systems.RenderSystem.flipFrame(SourceFile:99)
	at dgu.e(SourceFile:301)
	at dlt.e(SourceFile:1035)
	at dlt.d(SourceFile:648)
	at net.minecraft.client.main.Main.main(SourceFile:215)