The bug
The problem that blocks remain depending on the order of updating blocks of the fill command.
(Old name: /fill lava bug
Old description: When replacing water, lava and obsidian with lava with /fill, not all can be replaced.
I checked this bug in 1.12.2 and 1.17.1.)
How to reproduce
Create a space of 2 by 2 or more(Height is 1 or more)
Fill the space with lava (r1.png)
Put a block of water in the lava (r2.png)
Replace all with lava with /fill (r3.png, r4.png)
Related issues
Attachments
Comments

Seems similar toΒ MC-187732. Would this happen to describe your issue?

I expected what was going on.
I think the fill command places blocks and updates surrounding blocks in order from the north and east corners.

Obsidian is placed north and east of water.
Lava is placed south and west of the water.

The same result was obtained for cactus.
[media]
This is the same type of problem as MC-187732.

Can confirm in 21w37a.

Thank you for your report!
We're tracking this issue in MC-31100, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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