Quick question - if you move the connection from a 'bad' port to a 'good' port, does the situation follow the device, or remain with the same port? This should tell you if situation is related to EX4300 or to the external devices. If remains with port, then suggest you look and compare configuration of these ports, and also check that nothing extra inherited from Groups, if indeed you are using groups at all.
You also mentioned POE. So what is the attached device, AP or IoT device or what? Could it be expected that with no IP address, it sends no Ethernet frames?
Good luck. If this behavior continues, I suggest opening a TAC case, if you have not already done so.