Losing all printers in Sierra

Have just installed two latest Sierra security updates. Not sure that it is related, but now regularly losing all printers.

Have to reboot - printers come back - but not for long. Preferences says no printers available, apps can't find printers - both take ages looking for them. CUPS won't load in Safari - just hangs trying to load form localhost.

What can possibly wake up and remove all the printer information - and yet it all comes back after a reboot - for a while? Does all of the printer information live in a single file somewhere?