Let's try this (for research purposes): keep the lid off the pail for better air circulation. If you live where you can sun dry your laundry, try that too to see if you can kill a few bonus smelly bugs. And by that, I mean keep the inserts out ALL DAY! Put them out in the morning, leave them out in the sun ALL DAY even after they are dry just for some extra UV killage. UV wreaks havoc on bacteria and smells, but you need to keep the dipes out for a while.
Air circulation and sun may help the smell issue at the beginning, think of it as a preventative measure.
If you can, do a rinse-and-wring before you store the icky dipes awaiting laundry. Again, I know that's not always possible. Best thing for storage is to have rinsed but not soaking diapers, with air flow.
Try this for a couple of rounds and see if that helps.
Stripping is the last resort. It's harsh but it does the trick. You do want to minimize anything you can so you don't have to do this very much (like, ever).