Alamofire request is being cancelled

Question

Background

I am creating a series of requests to grab a chunk of a file. The chunk size stays the same so the number of requests may change depending on which file I am downloading. For smaller files, and thus smaller number of requests I seem to reliably succeed. However once my request chain reaches the 10+ ballpark I start to get an error.

Error

I am getting an error from what appears to be Alamofire.

Error code -999 cancelled.

Looking at other purposed solutions

From the searching I have done it seems that this occurs when either the session manager is deallocated or another request was kicked off before I received a response from the previous request .

I made my session manager static, as stated by some other posts to handle the deallocating issue, but I still get this error.

I don't think the next request is being called before the first finishes as my logs seem to be printing out in order and the failure is rather random. I would expect that the requests would overwrite quite reliably.

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Is there any thing else that causes this error code to occur?

Additional Logs

NetworkFilesClient.swift:351 - Error downloading chunk URL: MY_URL_HERE, 
Range: bytes=29360128-33554432, 
Error: Error Domain=NSURLErrorDomain Code=-999 "cancelled" 
UserInfo={NSErrorFailingURLKey=MY_URL_HERE, 
NSLocalizedDescription=cancelled, 
NSErrorFailingURLStringKey=MY_URL_HERE}

Answer 1

What works for me:

sessionManager.session.finishTasksAndInvalidate()

I put this at the end of my response handling. Why? No clue...