Something to keep in mind. One of your cameras might be going bad.. I had a Dahua 4mp AI camera fail in POE and took out all POE cameras that were connected on my POE NVR ports all other channels were online. When I connected the cameras to my POE switch again all POE devices went offline even ones that were already working on a different NVR.. In order to get that to work I had to reboot my POE switch. So didn't remember if any of them were POE+ so thought ok try on that Switch and this time rather then plug them all in and wait for them to come online all at one time. I did them one by one and sure enough my Dahua IP4M-N45EF63 caused my whole POE+ switch to shut down and had to reboot the switch.. After taking the bad camera apart I found that a SMD Common Mode Choke had failed and was the cause of issue. Lucky for me it damaged in a way that was a Open and only damage was the SMD common mode choke.. I have since repaired this camera and it is back in service now for the last 7 months without another failure so far..