Put the summary of the bug you're having here
What I expected to happen was...:
a fully completed functional map
What actually happened was...:
gray streaks were randomly set across the map (same goes for updating a map)
Steps to Reproduce:
1. create a map and or update an already existing map
2. see results
3. ...
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Thank you for your report!
We're actually already tracking this issue in MC-179858, so I've resolved and linked this ticket as a duplicate.
That ticket has already been resolved as Fixed. The fix will arrive in the next version or is already included in the latest development version of the game, you can check the Fix Version/s field in that ticket to learn more.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
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