Contact the manufacturer and supplier. Some of the additives will break from the emulsion and have to be remixed. Other times, external contamination/ bacteria/ large temperature swings can cause separation or odour. Many latex paints use ammonia as a pH adjuster during the latex reaction which can give a strong odor. Some may use mercaptans in the formulation. As an example of the odour many are familiar with, Natural Gas ( methane) is doped with mercaptan for consumer natural gas to allow easy leak detection and to get occupants out of the building.
The antimicrobials added during the formulation generally will last up to a year with the container unopened. Old paint or improper storage will accelerate loss of antimicrobial function. Contamination from the brush used after applying to the surface and repeatedly dipping in the can may overwhelm the antimicrobial. One reason to always pour from the supply container to a secondary container for painting and not dip the brush in the supply can.
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