stateManager is nil in iOS SDK for readFromSecureStorage

We are using the iOS SDK, we use the code
to save the state, we use the command
if let oktaOidc = oktaOidc {
stateManager = OktaOidcStateManager.readFromSecureStorage(for: oktaOidc.configuration)

to get the state manager back after the app is restarted. We are seeing the stateManager return as nil in some cases, and we can’t figure out why. Are there any circumstances when the read would not work?