Why do I sometimes see failures when performing HDCP Authentication?
This can happen if there is a mismatch in the DDC termination.
The HDMI Transmitter (TX) Subsystem v2.0 (Rev. 2) in Vivado 2016.3 and later contains additional logic to improve the robustness of the DDC interface for HDCP authentication in these conditions.
This is done by fixing the DDC state machine, which forces SDA data low in the last state.