You are right. I went back and read hdcp spec. Now I understand my confusion. What I experienced multiple times with hdcp and bad/low quality cable/connection was screen going blank for a short moment. I always assumed it was cryptography itself breaking apart, but the spec requires resetting connection in case of logged TMDS layer errors
" While the receiver may reach a determination
sooner, the receiver must determine loss of synchronization at least by the time it has detected 50
consecutive data island packets with ECC errors. The HDCP Receiver must either assert the
REAUTH_REQ bit of the RxStatus register or de-assert HDCP_HPD to the upstream transmitter
once it determines loss of synchronization. "
" While the receiver may reach a determination sooner, the receiver must determine loss of synchronization at least by the time it has detected 50 consecutive data island packets with ECC errors. The HDCP Receiver must either assert the REAUTH_REQ bit of the RxStatus register or de-assert HDCP_HPD to the upstream transmitter once it determines loss of synchronization. "