It isnt clear if it was a one off or could be repeated.Yes, It's hard to say is it serious or something like very rare case.
A single 5/5 isn't always something to be concerned with.
If the artifact is really bad it is enough, but when more subtle and
combined with very high settings you want better score / repeat result (IMO).
However, Joni Mitchell "Cool Water" is not a problem sample (at least I'm considering it as normal cd music),
and when someone notice a problem on normal listening using extreme mpc setting Q7 that is slightly worrying.
But it's probably very rare case and difference should be very subtle on Q7.
btw, nice to hear from you @shadowking