If you're balance is in "currently not collectible" (CNC) status, it doesn't mean that the debt is eliminated. It means that, at that point in time, the IRS doesn't believe that you can pay them and pay basic living expenses. If circumstances change, the CNC status is lifted. In the meantime, the IRS will always take any tax refunds owed to you each filing season until your balance is eliminated. This is completely normal. Your balance will also continue to accrue interest and penalties until it is either paid or the ten year statute of limitations is reached.
https://www.taxpayeradvocate.irs.gov/get-help/paying-taxes/currently-not-collectible/#:~:text=There%...