DIAGNOSIS Vinegar residue is trapped in the plastic or has degraded the filter. Plastic is porous and absorbs flavors.
FIX Discard the current filter. Wash the pitcher and reservoir with a mild dish soap and warm water. Rinse thoroughly. Soak all parts in a baking soda solution (1 tablespoon per gallon of water) for 30 minutes. Rinse again. Install a new filter and prime it twice.
IF THAT DIDN'T WORK The plastic may have permanently absorbed the vinegar. Persistent taste means you need to replace the pitcher components. The plastic is not designed for acidic cleaners.
HEADS UP Never use vinegar, bleach, or abrasive cleaners on any part of the system. It damages the plastic and voids the performance of new filters. Use only mild soap.