Restored DB Server Using FQDN Causing Distribution Issues
1, once your run the sp_Drop/addserver, most likely the system needs a start up if there is no other issues. You may also put the downtime into your consideration. 

2, If the problem is still there after restarting your server, you may disable the connection between your replica serves, restore each one individually, then set the replication on your new server .

3, You may also experience issues if your SP is old, refer to Microsoft for SP new release. 

Thank you,