Rain falls through any blocks in some spots

For anyone who opened their world in 20w17a and is still experiencing this issue in versions after 20w17a:
Try optimizing the world:

• Client:
  1. Select the world on the world selection screen
  2. Press the "Edit" button
  3. Select "Optimize World"
  4. Check "Erase cached data"
  5. Press "Create backup and load"
• Server: Start with --forceUpgrade --eraseCache

If you are still experiencing this issue after trying the steps above, please create a new ticket and attach the world (in the version before you opened it in the latest version of the game) as a zip file.