I've had similar symptoms with a number of P1214-E cameras, where the web interface was still accessible, but there was no video (video displays in the web interface would just be a grey box). A power cycle would bring it back every time (yay for managed PoE switches) but it's frustrating to have to do that repeatedly. Worse, the problem would only crop up every few weeks, so every time a fix was tried (default settings, new firmware, etc.) we'd have to just wait, sometimes a couple months, until it would manifest again.
I sent every log file to Axis, both before and after power cycle... the best they could come up with was MAYBE interference on the network line, which was a distinct possibility, since the runs all followed line voltage inside the center pole of giant fixed "umbrellas" on a restaurant patio, and the interface box was inside a housing at the top where all the heater and lighting wires split out (fortunately the lighting is all low-voltage LED)... and the most-affected unit is probably getting close to 300' from the switch.
Some others did it occasionally as well, and I swapped the interface boxes between a few of them, but the problem remained most prevalent at the same one. Also re-terminated the UTP, and removed a wadded mess of UTP where the A/V installer had not bothered to coil it properly after adding the speakers to the fixture. Finally I swapped the sensor module with another unit that had been working solidly... but still to no avail; with several weeks it was back to the same hijinks.
Since these are all in an outdoor (though completely covered) area near the ocean, I also opened up a few of the interface boxes to check for corrosion, but found nothing. But it did occur to me, the last time I did a swap, that maybe the jacks WERE still getting a bit of oxidation on the pins of either the 8P8C on the network connection, or the 6P4C on the sensor connection... so the last thing I tried was to add a bit of dielectric grease to all those connectors, then wrap the whole assembly in a freezer back along with a desiccant pack, squeeze the air out, and zap-strap them shut.
That was all within the last couple weeks, so now the waiting game begins again...