One of our iMacs is having serious connectivity problems. Both ethernet & wifi will drop internet access. Happens daily, randomly & repeatedly. The computer will still be visible on the LAN & can still access LAN stuff but it just drops internet. This does not happen to our other iMac which is using the same network etc. Sometimes forcing it to renew the DHCP lease fixes it, sometimes not. The iMac with the problem is a Retina, 27", late 2015 model running 10.12.3. This was never an issue before Sierra updates. Any help appreciated as I don't even know where to begin to try & troubleshoot as it doesn't make any sense to me.