Since #14007, the functional tests would run on Appveyor CI. However the tests would fail occassionally due to several reasons. Here is the list:

• ConnectionAbortedError: [WinError 10053] might be a race condition
  Maybe fixed by http: Fix HTTP server shutdown #14670
  For reference:
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19366470
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19344806

• PermissionError: [WinError 32]: found in feature_notifications. The test script delete the files before the notification command close the file.
  Maybe fixed by tests: Stop node before removing the notification file #14465
  For reference:
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19363071
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19342222

• OSError: [WinError 10022] An invalid argument was supplied: Unknown reason.
  One-off?
  For reference:
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19365696

• AssertionError: Block sync timed out: Unknown reason. Found in wallet_txn_doublespend
  For reference:
  Maybe fixed by qa: Always refresh cache to be out of ibd #15419
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19360284
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19334394
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/20031316

• PermissionError: [Errno 13] Permission denied: Unknown reason. Found in get_auth_cookie function
  Maybe fixed by tests: Possible fix the permission error when the tests open the cookie file #14788
  For reference:
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19324004
  https://ci.appveyor.com/project/DrahtBot/bitcoin/builds/19393533

If you find any fail that is not listed here. Please comment below.