the original poster said they were using GMAW-S.
with spray transfer Spray transfer- the two types of these discontinuities that I have experience with are: 1- shallow dish type "dimple". 2- throught hole "pipeing porosity.
Type 1- the solution that we've found that works is to trian the welder to filck the wrist to cause the electrode to in an opposing direction to the angle (lead or drag) used during travel - this seems ot not only encourage hesitation at the termination of the weld for filling the crater but also stops the "dimple" - this is of course after we verify that the parameters use aren't "starving" the puddle. see picture
Type 2- through hole is usually found when sealing a weldiall-around joint - theory we have is anything on the faying surfaces that can be vaporized -will be vaporized and the vapor will escape as the last liquid point of the weld - Clean seems to have minimize this in our shop
Hope I was helpfull