The filter is dead.
To keep active filters, they need to be swaped out every month or so if they're not kept in the sealed cans. The sealed cans have kind of a sardine can opener on them to open. Inside is the filter can, not sardines (unfortunately).
If against something like VX or the like, most of those can be absorbed through the skin anyway. The full MOPP getup is what makes it survivable.
Make sure there are no cracks or leaks in the mask. The best way to do this is to put your hand over the filter intake and breathe in. There shouldn't be ANY intake at all from anywhere on the mask. Not even a tiny tiny bit. Zero, none, nada.