You mentioned that you are certain it is now Firmware related and that you downgraded. But, I’m not seeing in any of your posts which version of the firmware you had\have the cams running. Also not clear which version you used to Flash back.
4.36.11.4679 is the latest V3 Production Release firmware available.
If the cam is inaccessible for a Flash reversion, have you considered entering the Beta pool and installing the 4.36.11.4847 Beta Firmware currently in testing, which I have been successfully running on all my V3 cams since it was released? This will allow you to update thru the standard OTA cam firmware update channels. You can then turn off future Beta update opportunities or leave the Beta pool. It is worth a shot so that you may not have to flash that cam.