Why Sync is auto stoped ?

I have read FAQ part of “What does it mean when Avast Sync shows the status ‘Paused’ or ‘Error’?” , but they are not the same reason like I have.

I do not have sign in https://id.avast.com, and I do not set sync passphrase

Hello Liu12,
sometimes we show those states when we’re releasing a new version so we need users to sign in again.
Can you please tell me more? You can’t sign in to sync service now?

Also please try:

  1. Reset the sync - secure://settings/resetSync. Please back up your bookmarks (just to be sure) and reset the sync. Try to sign in to sync afterwards.
  2. Try to Sign out and sign in again in secure://settings/syncSetup page.

Sorry for the inconvenience!

See if this works for you also:
https://forum.avast.com/index.php?topic=320388.msg1691253#new