So, if there was some issue that caused the local private key / flash to be corrupted, by say, a power issue, you might see this. I think we talked about it here:
Please make sure your power supply is operating as required, then:
You can generate a new key for the p1:
particle keys new --protocol rsa
You can then use your JTAG pins to copy the device.der key to address 34.
Make sure you send the key to the cloud to unlock the pinned key with:
particle keys send YOUR_DEVICE_ID device.pub.pem
There are some docs around this here: https://docs.particle.io/support/troubleshooting/key-management/photon/
Feel free to send me your external IP address, and your device_id, and I can check the logs as well to see if there is any other information there.
edit: it's also possible the server key became corrupted somehow, so replacing that would also be a good thing to test.