WatchConnectivity Swift 6 - Incorrect actor executor assumption

I am trying to migrate a WatchConnectivity App to Swift6 and I found an Issue with my replyHandler callback for sendMessageData.

I am wrapping sendMessageData in withCheckedThrowingContinuation, so that I can await the response of the reply. I then update a Main Actor ObservableObject that keeps track of the count of connections that have not replied yet, before returning the data using continuation.resume.

...
@preconcurrency import WatchConnectivity

actor ConnectivityManager: NSObject, WCSessionDelegate {
  private var session: WCSession = .default
  private let connectivityMetaInfoManager: ConnectivityMetaInfoManager

  ...

  private func sendMessageData(_ data: Data) async throws -> Data? {
    Logger.shared.debug("called on Thread \(Thread.current)")

    await connectivityMetaInfoManager.increaseOpenSendConnectionsCount()

    return try await withCheckedThrowingContinuation({
      continuation in
      self.session.sendMessageData(
        data,
        replyHandler: { data in
          Task {
            await self.connectivityMetaInfoManager
              .decreaseOpenSendConnectionsCount()
          }
          continuation.resume(returning: data)
        },
        errorHandler: { (error) in
          Task {
            await self.connectivityMetaInfoManager
              .decreaseOpenSendConnectionsCount()
          }
          continuation.resume(throwing: error)
        }
      )
    })
  }

Calling sendMessageData somehow causing the app to crash and display the debug message: Incorrect actor executor assumption.

The code runs on swift 5 with SWIFT_STRICT_CONCURRENCY = complete. However when I switch to swift 6 the code crashes.

I rebuilt a simple version of the App. Adding bit by bit until I was able to cause the crash. See Broken App

Awaiting sendMessageData and wrapping it in a task and adding the @Sendable attribute to continuation, solve the crash. See Fixed App

But I do not understand why yet.

Is this intended behaviour? Should the compiler warn you about this? Is it a WatchConnectivity issue?

I initially posted on forums.swift.org, but was told to repost here.