If you have them, they are likely in high-temperature areas where only metal lock-nuts are called for. Don't try to swap them for a different type.
 
Remember that in the scheme of things, this is just a limited batch from one of many suppliers. Our company material engineers knew about this issue a year ago and fortunately, of the millions of these nuts we go through, we don't procure from them.

I don't know how easy it would be to track down the source of the nuts that was supplied to Spruce or Van, but there is not a fundamental issue with this type of nut.
 
If you look at the spec on these nuts, you'll see that they are direct substitutes for the more common types.

Dave