I realize this is a very old post, but just in case you are still out there Mic_n, did you ever resolve this problem, as I am having the exact same one. This is on all three boards we have built so far. The first board we built did get to 8...
I'm trying to get a custom board based on T4.1 up and running. I'm at the 8 blink stage:
8 Blinks = Unknown IMXRT Chip
The IMXRT chip responded, but with an unsupported JTAG ID. This error can happen if IMXRT AD_BO_08 is not connected to MKL02...