nozzle clog

After printing 1 job I have to use the atomic method to start another print. Doesn’t matter if its a 20 hour print or a 15 minute print nozzle is always clogged when I go to print again. Also time in between prints doesn’t matter. Happens with both .4mm .6mm nozzles. Using color fab filament or ultimaker fillament clogs with both. Any theory’s out there on this problem?