We are using the PTN3460 on an add on CPU board that has an Intel Braswell CPU, where it sometimes completely fails to answer to accesses via the eDP side after powerup. This is very temperature dependant, so the lower, the more often it happens, but still keeping within the 0 - 70C parameters.
Each time this happens, it is possible to see a small difference on 2 bytes on the SMBUS bus side, however, these bytes are not documented, and marked to be in a reserved region (0x99 - 0xD6) according to AN11128.
The bytes in question are 0xC0, that on successfull starts contains 0x04, and 0xC3, that on success contains 0x03.
On failed bootups, both these bytes instead contains 0x00.
It would be interesting to get confirmation if the normal values of these bytes (0x04, 0x03) are some sort of indication registers for a successful (e)DP connection, as it then might more point to the eDP transmitting side being the cuplrit somehow.