Not Enough Witholding?

My husband and I always file joint returns and have always had a refund. We both put married joint on our W4s and claim zero dependents, I double checked both W4s to make sure. When I import my W2, TT estimates a return of $1006. I made roughly $45k, and had roughly $3k in withholding. When I import my husband's W2, suddenly we owe $2200 instead of a refund. He made roughly $32k, but his W2 says only $500 was withheld?! This has never happened before and he's been with the same company for three years, no changes to his W4 at all.

 

I mean clearly I'm assuming the issue was not enough was withheld from his checks throughout the year, but I don't understand why or how. Like I said W4 states married joint, zero dependents, zero additional amounts withheld. Does anybody have an idea as to what happened?! I should've looked at his paystubs throughout the year (he doesn't pay much attention to them, or at least not these parts of them). That's on me. I just don't get why more wasn't withheld.