We tested a potential Aunt for my husband and the results came back 1992 Cm. We know this falls into the range we expected however, I immediately realized she has matches that she doesn't share with my husband the first closest unshared match being a 2nd cousin. I checked his tree and he decends from her mother line. All the unshared matches who have trees are on her moms side. Is she his half sibling? Are we missing something? I cannot get a straight answer. Please do not direct me to the charts or gedmatch..etc.. Should an aunt share a 2nd cousin with her nephew?
Not necessarily. And sorry, you can't work this out unless you use the chart !
His aunt's (let's call her A) second cousin (let's call them C) isn't your husbands (H) second cousin, as you'll see if you follow the guidance at Determining relationship (e.g. number of removes) with cousin?.
Once you've worked out the relationship of her second cousin to your husband, you may well see from the chart that he could potentially share zero DNA with C but still be related to him. Or maybe not -- a shared amount of DNA of zero could mean 'not related' or 'the luck of the draw meant they inherited different DNA from a common ancestor'.
Because you haven't given us the amount of shared DNA between A and C, we don't know for sure that C is A's second cousin -- there are a number of other relationships that would shared the same amount of DNA and you need to consider all of them, using the chart
However let's assume A and C are second cousins and so share great-grandparents; H and C will be second cousins once removed because of the generational differences. And second cousins once removed typically share between zero and 316cM of DNA.
Updated: You've now told us that A and C share 218CM, and the tree confirms they are full 2nd cousins. It's still possible that H and C will share no DNA even if they are related; and (depending on how A is related to the other matches that H doesn't share, that H will share no DNA with them even though he may be related to them.)
You might want to explore the What Are The Odds Tool which was created for just this type of situation.