this was a bug in 20w17a and I tried loading the maps back in and I still have the gray lines
Related issues
Attachments
Comments

[media]

Once the map loaded in 20w17a, it will of course stay the same later on. If you have a backup (before 20w17a), load it with 20w18a. There won't be this bug then.
Check the description of MC-179858.