Here is a list of steps to troubleshoot Active Directory Trusts not synchronizing:

1. Ensure that the trust relationships are still valid – Check that all the domains involved in the trust relationships still have the trust setup and active. In the source domain, you can do this by running the command netdom trust [Destination Domain] and checking for the homogenous and respectMutual values.
   
2. Verify that Trust Passwords are disabling correctly – Ensure that the trust passwords are being correctly disabled and when trying to access the trusted domain, the new password is presented.
   
3. Verify that the right trust passwords are set – Make sure that the trust passwords negotiated across the domains match. Use a tool like trustmon to validate the trust passwords set across the domain (Trustmon is a tool available as part of the Windows SDK).
4. Check that the source domain is able to connect to the trusted domain – Run the command net use \\\IPC$ to test that the source domain can authenticate with the trusted domain. If this works, you should be able to see the drive mapped correctly to the connected share, otherwise you will receive an Access Denied error.
5. Check the status of the trust relationship in the destination domain – Check the destination domain to verify that the trust relationship with the source domain is still active. In the destination domain run the command netdom trust [Source Domain].