could you tell me why this WU as not been credited yet ?

Remember that we're still in testing...
Explaining this is easy: the workunit has (somehow,
most probably during some tests) been flagged with
"need_validate = no" although the "canonical result"
has not been found.
No validation run, no canonical result, no credits.

This, in production, should never happen, of course.
But nothing is lost - only credits may be a bit delayed.

Thanks for pointing this out!

Steffen