0xAA55

You are tried to just update the server jar file to 1.14(or newer), but your saved world file was kept as it is.

My server also has the same symptom which was lagging extremely, when I updated the jar file from 1.13.2 to 1.14.2 directly.

I found that if any player moves nearby a chunk which is old (not generated by 1.14.2 server), the server lags as all of the players' movement 'undo' and the server's console shows 'Player XXXXX moved too quickly'. Once the server loaded all of the old chunks that are near enough to any player, the server didn't lag anymore.

Due to these, I guess that the server was trying to upgrade the old chunk data to the newest version, and the conversion is very slow, so the server lags. When the conversion has been done, the server runs smoothly.

I also changed my server running script to let it restarts every 3 hours. After the restart, the server runs extremely smoothly a while.

You might want to try to upgrade all of the saved world files to newest by using the client's upgrade world option.

This is still an issue happened in my 1.13.2 server. When a player joins in my server, it may happen. When it happened, all of the players cannot play, and we can only wait for about 2 or more minutes for the server responding.

Also if a player jumps into an End portal, it may happen. When we wait until the server works, the player logs in, he(she) will be in the End and the coordinate is the same as the End portal, resulting a player dropped to the void – die and lost all of the items.

It's quite funny that the dead player goes to the hell.

Also the animation of the water surface of waterlogged stairs can be affected by the nearby water blocks, which shouldn't affect the 'stair water' through the stair, see 2018-03-15_05.23.46.png.

Snow Golems don't have feet, so they shouldn't play footstep sound.

You may need to know one of the gamerule which called disableElytraMovementCheck that can be changed by the operators of the server to let you fly better.
You may fly too fast, and the network may be very laggy, so the server thinks you may using a modded client to cheat (to do teleportation which shouldn't be happen when you are playing survival or you are not using commands). Then, the server resets your position so you can't move. Also if you runs too fast, the server also resets your position.
This is the builtin anti-cheat engine of Minecraft. It causes you suffered from this.

Also in Minecraft Java Edition 1.12.2.

I put an unnamed item to the anvil, and delete the original name of the item, I see the output's name is the first character of the original name.

I think the trident does the same way. I tried to throw a trident with Channeling enchantment to an Enderman, the trident bounced off to the ground, the Enderman teleported away, and the Lightning bolt hits the teleported Enderman.

This bug still exists in Minecraft 1.12, I'm sure.
This should be reopened.

Mine is:
Reported exception thrown!
f: Ticking screen
at bhm.t(SourceFile:1606)
at bhm.ax(SourceFile:964)
at bhm.a(SourceFile:404)
at net.minecraft.client.main.Main.main(SourceFile:123)
Caused by: java.lang.NullPointerException
at io.netty.bootstrap.Bootstrap.checkAddress(Bootstrap.java:358)
at io.netty.bootstrap.Bootstrap.doResolveAndConnect(Bootstrap.java:180)
at io.netty.bootstrap.Bootstrap.connect(Bootstrap.java:162)
at io.netty.bootstrap.Bootstrap.connect(Bootstrap.java:143)
at brt.b(SourceFile:241)
at brt.a(SourceFile:45)
at brt$1.a(SourceFile:144)
at go.l(SourceFile:382)
at brt.a(SourceFile:254)
at bmq.e(SourceFile:115)
at bhm.t(SourceFile:1596)
... 3 more

I'm sorry for that, and I had used search function to find the keyword 'xray', but I only found the old post: https://bugs.mojang.com/browse/MC-1769
Maybe my English is too bad for creating tickets...

I also have this issue, if I click `multiplayer' in the main menu and quickly enter a server, this bug will happen.
But if I click `multiplayer', and wait a second, I can get into the server and play normally.

I already turned it off, but I still keep jumping here automatically.

If you try to play this game under a bad network (ping 400 ms).
It should to be say as a bug because under a bad network, OVERWATCH runs properly, MINECRAFT does not.
I think "xxx moves too quickly" should be an anti-cheating mechanism. But look at the average speed, I even walk very slow, I will be occasionally teleport back.

I am the owner of the server, and the server is NOT OVERLOADED because it DOESN'T tells "Did the system changed or overloaded ....."
It's a CentOS 6.5 x86-64 server with 32GB RAM, there's 4 players in the game, no mod installed.

Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 8
On-line CPU(s) list: 0-7
Thread(s) per core: 2
Core(s) per socket: 4
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 60
Model name: Intel(R) Xeon(R) CPU E3-1230 v3 @ 3.30GHz
Stepping: 3
CPU MHz: 3292.520
BogoMIPS: 6585.04
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 8192K
NUMA node0 CPU(s): 0-7