Hi, first please check, whether Avast Antivirus has granted all permissions it requires.
If the problem persists, please remove your device from My Avast and then log it back.
If it doesn't help either, uninstall all your Avast applications (Avast Secureline, Avast Mobile Security, Avast Cleanup, Avast Battery Saver etc.), then open Settings of your device, go to "Accounts & Sync" and make sure that Avast is not on the list of the accounts (if it is then some Avast app is still installed). Once Avast account is removed, please try installing Avast Mobile Security from Google Play app store again and connect it to my.avast.com account.
