Creating or updating maps result in them getting random stripes in worlds made before the 1.16 snapshots, it usually happens on world generated terrain and not on user made structure likes its shown on the screenshot.
To reproduce open the world and update one of the maps
World with the issue: https://drive.google.com/file/d/1mjAMK0-M1fjDXzPahNPa0LQAsmsjRkR2/view?usp=sharing
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We do not have enough information to find the cause of this issue.
Please attach the affected (zipped) world file (Version 1.15.2). If the file size is too large, please upload it somewhere else and then link to it here.
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i have added the affect world

This is an already known issue:
when you select the world, click on "modify" > "optimize world" > "create a backup and optimize"
wait until the process has ended and open the world, the maps should update back to nomal
Thank you for your report!
We're tracking this issue as MC-179858, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as Fixed. The fix will arrive in the next version or is already included in an available version of the game, you can check the Fix Version/s field in that ticket to learn more.
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