(In reply to comment #54)
> However if I set pi->dynamic_ss to false the lockups disappear, it also
> works with dynamic_ss set to true and pi->mclk_ss set to false.
>
So this seems to point to a spread spectrum mischief. I don't know if
dynamic_ss automatically applies to mclk but it seems to, since disabling
spread spectrum only for mclk solves your problem. We could suspect that at a
given frequency, we have a problem restoring the original message / clock (the
higher we get, the harder it is) until at some point it becomes unreliable.

I should be able to test it later tonight to confirm if this fixes the bug on
my side too.