When is it ok to skip the Profession of Faith?

I’ve noticed that our priest sometimes skips saying the Nicene or Apostles Creed during our Mass after the sermon. Why??

If its a weekday Mass then he is correct to skip the Creed since it is not part of weekday Masses (outside of certain feast days). If its a Sunday Mass then he is incorrect to skip the Creed because it is supposed to be said at Sunday Masses. It does not invalidate the Mass in any way, but the action of omitting the Creed on a Sunday is illicit.

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