Session lifecycle management with AlamoFire

Question

My app has been reporting an unreproducible crash due to this error:

Task created in a session that has been invalidated

Other posts with this issue are usually calling invalidateAndCancel() or finishTasksAndInvalidate() on a Session and then reusing that Session. In this case we never explicitly call invalidate and the only place I see invalidation occurring is internally within the AlamoFire framework when the SessionManager is deinitialized.

My use case is a custom background SessionManager with a hardcoded sessionIdentifier to poll an S3 url and render a JSON once the URL returns a valid response.

Relevant code:

class Poller {
    private let jsonRequestClient: JSONRequestClient

    init() {
        self.jsonRequestClient = JSONRequestClient("com.app.poller")
    }

    private func scheduleRequest() {
        scheduledTask = ScheduledTask(timeIntervalSeconds: config.getPollingInterval())
        scheduledTask?.eventHandler = getResponse
        scheduledTask?.resume()
    }

    private lazy var getResponse = {[weak self] in
        guard let strongSelf = self else { return }

        strongSelf.scheduledRequest = strongSelf.jsonRequestClient.requestFromPath(path: strongSelf.urlString, params: [:], success: { response in
            strongSelf.handleSuccess(response: response)
            strongSelf.scheduleRequest()
        }, failure: { error, httpStatusCode in
            strongSelf.scheduleRequest()
        })
    }

}

class JSONRequestClient {
    private let sessionManager: SessionManager

    private init(sessionIdentifier: String) {
        let config = URLSessionConfiguration.background(withIdentifier: sessionIdentifier)
        self.sessionManager = Alamofire.SessionManager(configuration: config)
        self.sessionManager.retrier = retrier
        self.sessionManager.startRequestsImmediately = true
    }

    @discardableResult func requestFromPath(path: String, params: [String: String], success: @escaping (DataResponse<Any>?) -> Void, failure: @escaping (_ error: Error?, _ statusCode: Int?) -> Void) -> DataRequest? {
        var urlRequest = URLRequest(url: url)
        return sessionManager.request(urlRequest)
    }
}

I have noticed that in some cases, multiple of these Pollers can be created which would cause multiple SessionManagers to share the same id. I'm planning to resolving this by creating a singleton for the JSONRequestClient, which is a best practice mentioned in AlamoFire docs. However, from my testing, reusing the same sessionId on multiple Sessions does not cause this crash. Another scenario I have tested is creating multiple Sessions that share a single sessionId, then invalidating one of the sessions and attempting to make a request using the other one, this also did not repro the crash.

Some Questions:

Is this likely being caused from multiple SessionManagers sharing the same id?

Is it possible that after a SessionManager has been deinitialized the invalidated session is still referenced in AlamoFire? My code does not reference the Session and only uses the SessionManager so I would not think it's possible.

Another possibility I considered was a retain cycle in my Poller's eventHandler scheduling tasks causing it to call jsonRequestClient.requestFromPath() after the SessionManager has already been deinitialized. I added some safeguards (guard let strongSelf=self else { return }) to prevent this but maybe it's still happening?

I'm stumped so any ideas are appreciated, thanks!