It sounds like the battery has been discharged and damaged. I’m not sure why that happened. Storing them at 3.8v/cell should have been fine. I don’t know what a PRM module is and whether that had an influence. If it’s open loop it shouldn’t, as you wrote.
If it’s swollen, it’s likely damaged and should be properly disposed of. Charging at that point can be dangerous, so I wouldn’t recommend it.