Cameras Losing Connection

I am looking to see if anyone has some advice with a problem I have with a couple of installs where I have 8 Axis cameras with a NUUO NE-4160 NVR. I have issues with cameras losing connection for about a minute and then reconnect again. This happens frequently. What should I be looking for?

Lawrence, do all cameras go offline at the same? Or do some cameras randomly go offline and then others later on?

Have you verified that your PoE power source (switch, midspan, etc.) is providing sufficient power for all cameras? What is your PoE power source (model)?

They seem to disconnect randomly.

The switches I have been using are the HP model JE007A or the TP-Link TL-SG2424P. Systems with both of these switches are doing the same thing.