Weird crash: missing symbol Swift.AsyncIteratorProtocol.next()

I got several reports about our TestFlight app crashing unconditionally on 2 devices (iOS 18.1 and iOS 18.3.1) on app start with the following reason:

Termination Reason: DYLD 4 Symbol missing Symbol not found: _$sScIsE4next7ElementQzSgyYa7FailureQzYKF (terminated at launch; ignore backtrace)

The symbol in question demangles to (extension in Swift):Swift.AsyncIteratorProtocol.next() async throws(A.Failure) -> A.Element?

Our deploy target is iOS 18.0, this symbol was introduced in Swift 6.0, we're using latest Xcode 16 now - everything should be working, but for some reason aren't.

Since this symbol is quite rarely used directly, I was able to pinpoint the exact place in code related to it. Few days ago I added the following code to our app library (details omitted):

public struct AsyncRecoveringStream<Base: AsyncSequence>: AsyncSequence {
    ...
    public struct AsyncIterator: AsyncIteratorProtocol {
        ...
        public mutating func next(isolation actor: isolated (any Actor)? = #isolation) async throws(Failure) -> Element? {
            ...
        }
    }
}

I tried to switch to Xcode 26 - it was still crashing on affected phone. Then I changed next(isolation:) to its older version, next():

public mutating func next() async throws(Failure) -> Element?

And there crashes are gone. However, this change is a somewhat problematic, since I either have to lower Swift version of our library from 6 to 5 and we loose concurrency checks and typed throws or I'm loosing tests due to Swift compiler crash. Performance is also affected, but it's not that critical for our case.

Why is this crash happening? How can I solve this problem or elegantly work around it?

Thank you!