Report on April 13, 2019 Starts here

   This world has been created on 19w08a, and has been updated into almost every single snapshot after, where I have fallen back two times because of barrel ticking (MC-145031), and chunks (not supposedly) being regenerated (MC-147800), meaning that the world had been on a newer version then back to 1 older version backwards (if it makes a difference). After the second falling back (1.14 pre1 back to 19w14b because of chunks regenerating), MC-142134 has also escalated from affecting around 20% of the light sources to 100% of the light sources (yes, not a single light source from the top to the bottom of the world, lava included was providing light).

  Now the server has been upgraded to 1.14 pre2, but every time a player joins the server, within moving a few blocks of time or instantly, the server experiences "Exception in server tick loop" and crashes, rendering the world completely unplayable.
*Edit: my world is also more than 1GB in size, so please tell me if it is needed and Ill find a way.
*Edit: the second falling back is actually not a falling back as I only loaded in a backup that was last used, 'cos falling back would keep the regenerated chunks. But I am not sure how MC-142134 escalated if no environmental changes (server jar file and it was the same world last used for that version of server jar file) were present (anywho, that lighting bug triggers almost completely randomly too (except for but not limited to when player exits/unloads the chunk improperly: client crashes, server crashes))
*Edit: I was to create an issue right when this happened yesterday, but the site seemed to be down (at least for me), I also used the search function for "Exception in server tick loop" that affects 1.14 pre2 and could not find any.

 Report on April 13, 2019 Ends here

 Report on April 16, 2019 Starts here

1.14 pre3 is out: Still fails to optimize or be force upgraded. World may be corrupted but there were no cause to it.
Story in detail, I attempted upgrades through these versions:
*(Parentheses mean backup made without optimizing before the upgrade)
*[Square brackets mean action taken but no backup made after the upgrade]
(A) 19w08a to 19w08b
(B) 19w08b to 19w09a
(C) 19w09a to 19w09a
(D) 19w09a to 19w11a
(E) 19w11a to 19w09a (Fallback due to barrel ticking MC-145031)
(F) 19w09a to 19w09a
(G) 19w09a to 19w12b
(H) 19w12b to 19w13a
(I) 19w13a to 19w13b
(J) 19w13b to 19w13b
(K) 19w13b to 19w14a
(L) 19w14a to 19w14b
(M) 19w14b to 19w14b
[N] 19w14b(from after (M)) to 1.14pre1 (Optimization succeeds, reset some chunks due to MC-147800, update world trashed)
(O) 19w14b(from after (L)) to 1.14pre2 (Optimization fails at 52% in singleplayer)
[P] 19w14b(from after (M)) to 1.14pre3 (Optimization fails at 34% in multiplayer, 52% in singleplayer)
[Q] 19w14b(from after (M)) to 1.14pre3 (Optimization fails at 7% in multiplayer)
[R] 19w14a(from after (K)) to 1.14pre3 (Optimization fails at 68% in multiplayer)
[S] 19w14b(from after (M)) to 1.14pre3

*Note: All worlds up to (M) work perfectly with noted bugs but no sign of corruption in their own versions, but recognized as corrupted (failed) in 1.14pre2 up
*All these backup worlds add up to a total of 13.3 GB so tell me which one to upload if one is needed.
Conclusion and suggestions:
   I believe some parts of the world is corrupted, in a way that up to 19w14b ignores, but that 1.14pre1 decides to regenerate those chunks, but 1.14pre2+ decides to fail the optimization. Again the worlds work perfectly fine (with noted bugs) up including 19w14b, but optimizations fail or regenerate chunks after 1.14pre1.
  This means the determination of whether a world is corrupted is inconsistent in different versions and it should not be like so. Now it is immensely difficult to find out in which of the upgrades did anything go wrong. Also it would have been better if optimization fixes the corruptions in worlds, unless it is too corrupted.
Temporary/Permanent Solution
  [S] Done without optimization. Some progress is lost but recoverable and just annoying.

 Report on April 16, 2019 Ends here

---- Minecraft Crash Report ----
// My bad.

Time: 4/12/19 9:23 PM
Description: Exception in server tick loop

java.util.concurrent.CompletionException: m: Loading NBT data
	at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
	at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
	at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1592)
	at agf.h(SourceFile:135)
	at agf.p(SourceFile:114)
	at vd$a.p(SourceFile:438)
	at vd.d(SourceFile:194)
	at net.minecraft.server.MinecraftServer.aW(SourceFile:708)
	at net.minecraft.server.MinecraftServer.p(SourceFile:696)
	at agf.bf(SourceFile:99)
	at net.minecraft.server.MinecraftServer.o(SourceFile:680)
	at net.minecraft.server.MinecraftServer.run(SourceFile:636)
	at java.lang.Thread.run(Thread.java:748)
Caused by: m: Loading NBT data
	at ib.a(SourceFile:444)
	at ib.a(SourceFile:81)
	at ib.a(SourceFile:438)
	at ib.a(SourceFile:81)
	at im.a(SourceFile:113)
	at im.a(SourceFile:78)
	at im.a(SourceFile:74)
	at bxs.d(SourceFile:53)
	at us.e(SourceFile:637)
	at us.f(SourceFile:412)
	at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
	... 10 more
Caused by: java.io.UTFDataFormatException: malformed input around byte 5
	at java.io.DataInputStream.readUTF(DataInputStream.java:656)
	at java.io.DataInputStream.readUTF(DataInputStream.java:564)
	at ib.b(SourceFile:431)
	at ib.a(SourceFile:78)
	at ii.a(SourceFile:65)
	at ib.a(SourceFile:438)
	... 20 more


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- System Details --
Details:
	Minecraft Version: 1.14 Pre-Release 2
	Operating System: Linux (amd64) version 4.15.0-47-generic
	Java Version: 1.8.0_202, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 798686136 bytes (761 MB) / 2034761728 bytes (1940 MB) up to 3817865216 bytes (3641 MB)
	JVM Flags: 2 total; -Xms128M -Xmx4096M
	Player Count: 2 / 20; [vg['VegetaI'/692, l='world', x=62.28, y=9.00, z=134.30], vg['Exit___'/1603, l='world', x=-140.72, y=71.50, z=-194.48]]
	Data Packs: vanilla, file/double shulker shells v1.0.0.zip (incompatible), file/OnePlayerSleepV2_5.zip (incompatible), file/more mob heads v1.2.0.zip (incompatible), file/Hermitcrack.zip (incompatible)
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)