[MC-192276] By doing something in my world it resets to how it was before a few minutes if I enter the nether and return to the normal world.

For example, in my world I put blocks to do something, then I enter the nether to do things in there, and when I return to the normal world the blocks I put disappear, as if the world was reset to how it was a few minutes ago. I already tried with versions 1.16.1 and 1.16, but both errors appear. It seems to be an error because my world generated it in 1.15.2 and updated it to 1.16.1.

Failed to save chunk 35,37
java.lang.NullPointerException
	at chv.a(SourceFile:413)
	at chv.a(SourceFile:359)
	at yp.a(SourceFile:716)
	at yp.e(SourceFile:388)
	at yp$$Lambda$4795/602747026.accept(Unknown Source)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
	at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
	at java.util.Iterator.forEachRemaining(Iterator.java:116)
	at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
	at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
	at yp.a(SourceFile:385)
	at zb.a(SourceFile:321)
	at zd.a(SourceFile:704)
	at net.minecraft.server.MinecraftServer.a(SourceFile:569)
	at eoz.a(SourceFile:85)
	at net.minecraft.server.MinecraftServer.v(SourceFile:672)
	at net.minecraft.server.MinecraftServer.a(SourceFile:256)
	at net.minecraft.server.MinecraftServer$$Lambda$3948/466841626.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:745)