This has nothing to do with cryptographic security or predictability.

This is about whether the output of the PRNG passes statistical tests for randomness. In a previous blog post by John D. Cook we saw that it failed the PractRand statistical test suite [1], and now we see that it also fails the older TestU01 suite, too.

When Xorshift128+ and Xoroshiro128+ were launched, they were claimed to be statistically excellent. Those claims have been shown to be false.

[1] https://www.johndcook.com/blog/2017/08/14/testing-rngs-with-...