I saw this issue with both the ADV7630 EVAL board and our prototype board.
It seems I have to wait until a source is detected on one of the Rx ports before writing the EDID to the internal RAM.
If I write the EDID while the Rx ports are empty, no EDID is read when a device is plugged in.
The only way I saw to work around this is to provide 5V to PortC's RXC_5V pin before writing the EDID.
How can I have the EDID available before a source is plugged into an Rx port?