Chased a similar bug in a KDF once and only caught it by histogramming the 16 bit draws, statistical suites never flagged it.
Your suites didn't even do a https://en.wikipedia.org/wiki/Kolmogorov%E2%80%93Smirnov_tes... which is what you did?
Your suites didn't even do a https://en.wikipedia.org/wiki/Kolmogorov%E2%80%93Smirnov_tes... which is what you did?