Maps show stone-like pattern despite it not being there

This is just a theory but maybe it ties in with the "underground rain" bug? It seems like some parts of the map simply ignore the surface blocks and might look for the next one right under some air blocks, in this case it could show caves - rain could behave similarly, bypassing the actual ground and only falling down in the caves

Had the same problem. This affects not only maps but block behaviors themselves. If you see rain in this world you should be able to see it going through some solid blocks. When those blocks are removed and placed back - they behave normally again. This must be due to the new block storage tweaks in the snapshot.

I do as well after updating and I am on java edition and this is super annoying and needs to be fixed. It also does this with new maps in the world.

this is indeed the same bug as "underground rain"  as seen at https://bugs.mojang.com/browse/MC-180090 and probably others

worlds from before 20w17a have their heightmaps messed up when loaded in 20w17a. Can see with f3: the S and M values (for WORLD_SURFACE and MOTION_BLOCKING) are just completely random values. A world newly created with the new snapshot does not show this issue for me.

also beacons can pass through these blocks

I hope this is also the only issue with what's causing my ice farm to grow oddly in lines. 😛  screenshot

This is still not fixed as of 20w18a, still happening to me.

It is fixed if you reload the world from before 20w17a. Now it would be nice to be able to "reset" the heightmap from a world corrupted by 20w17a (commands or external editor) but I don't know how to do that, sorry.

As far as I'm aware, worlds opened in 20w17a will continue to be affected by this issue. Optimizing the world will probably fix that for worlds opened in that version.

I confirm that optimizing the world, with "erase cache" checked, fixes the world, thanks 🙂

How do you "optimize" the world on a server ?

Start the server with the command arguments --forceUpgrade --eraseCache.

Im having this issue and I never used 20w17a. Iv'e only used 20w18a

Dear, Bartosz Bok (Assignee), 
@unknown  (Last dev who responded), and whom else it may concern,
This is still a major Bug in Snapshot 20w18a, as shown in the pictures I just added to this report.

When player walks/ flies around to update their map(s), this Bug occurs.

My system/version is MC Java Snapshot 20w18a  Windows 10 version 1909.

Please Have this Bug Re-Opened and maybe check it more thoroughly during that time. I'm not trying to be rude when I say that, its just that in my 3.5 years (and counting) of playing Minecraft, I've seen Bugs get fixed and thought to be long gone, resurface after a long time, or they somehow get added to new updates. I am not at all saying that you moderators and developers are bad, y'all are excellent at what you do. That's the truth. The fact is: No One Is Perfect (Except our Lord God Almighty ( If you believe in Him. No Offense if you don't.)) and it's just our nature for things like this to creep in sometimes.

Thank y'all for all that you do,

JAG

so how do i fix this yes i read your messages i dont know what you mean by Start with --forceUpgrade --eraseCache how do i do that where do i do that{{ is it a button somewhere do i type it somewhere. i use aternos to host my server do i type it in console or the game. do i use the .minecraft files that came with the game. what do i do help.}}

Can confirm that starting server with --forceUpgrade and --eraseCache fix the maps. I didn't update the entire map, but you can see that the area within my range is fixed.

With @Josiah Abram Guthrie on this one, still appears to be an issue with 20w18a. Maps created with an empty map or attempting to regenerate existing broken maps is not fixing them (running server). 

Please read the large yellow/red box in this ticket's description. Worlds you have opened in 20w17a will remain broken until you fix them. Additionally, in order to get the maps to render properly, you need to explore the affected areas again.

yeah i read the yellow box but where do i do that for server

Just want to confirm that the given solution worked successfully and my maps are back to normal.

Thanks for the help

JAG

@unknown, it says in the yellow box:

• Server:

  1. Create a backup by copying the world folder

  2. Start with --forceUpgrade --eraseCache

ty for the info but need the step to do if you upgrade the server version from snapshot 20w16 a to 20w17a then to 20w18 a?

Whenever you load a world in 20w17a, it will be broken and needs to be repaired.

If you skip 20w17a, the error will not occur.

I have a server started /w 20w07a on VPS /w Ubuntu. A few days ago, I started in 20w17a (the maps were normal) and then now I'm playing in 20w18a (today, playing the last snapshot, I saw that maps were corrupted., I did as you say (Start with: --forceUpgrade --eraseCache), but the maps are still bugged, can someone help me?

After running --forceUpgrade --eraseCache, you have to hold the maps and revisit the area.  They will update without the grainy texture.

i have done all and the map in my hand is the new one the map ind the frame is the old one that whas ufter updating it to show changes i made the map in my hands whas just created and have the same textur banner props what have  i make wrong ? playing on a multiplayer server 20w18a and the server owner have dowloadet the map the stoped the server make the edit over singelplayer and reuplodet the map to the server so i think the map issue sholld not more exist after all steps are done. the other maps parts still ok then i have never update them.

I fixed the issue following the steps above. However, I had to (re)explore the area carrying my maps to (re)paint them.

I don't understand how to start with  --forceUpgrade --eraseCache on my server. Is that a command? Can someone explain?

Yes, append these command line arguments to the command you usually start the server with. After you have started the server with these arguments once, you can remove them again. Note that it might take quite a while for the server to optimize the world.

This bug still hasn't been fixed and now it's 20w21a. I've reported yesterday and I hope someone fix this immediately. 

i optimised this world a while ago but im still having trouble with the lines
download for my world:
http://www.mediafire.com/file/09fdrmnlbwn1l2g/world_upgrade_fixed.zip/file

You need to check "Erase cached data" on upgrade screen, otherwise problem will persist

I followed the steps to fix the bug, but my game keeps crashing when I try doing that. My world is 2.72 GB.

I'm confused by the lack of explanation of a fix for servers what do I have to do?

It's clearly explained in the description.

all it says is make a backup --forceupgrade --erasecache I don't know what that means, are they commands? where do I put them?

it seems what the problem is is that in random areas it shows the second highest block that has air above it. IDK if this with helps anything.