couldNotUploadFile Error with status code 409: Upload-Offset conflict

I'm using TUSKit with Supabase storage (an S3 wrapper), and for the most part it's working fine except the case where I try to upload a large file (~1gb) while repeatedly backgrounding and foregrounding the app on my phone, either by swiping to the Home Screen or locking my phone. It's inconsistent, but after a few times doing that I get a couldNotUploadFile error with an underlying 409 status code error, and digging into the upload method in TUSAPI and printing the raw response data, it says "Upload-Offset conflict".

How can I debug this? Is it an issue with my usage of TUS, the TUSKit iOS SDK itself, or is it possible this is a problem with Supabase's TUS protocol implementation?

Here's the full error:

uploadFailed: couldNotUploadFile(underlyingError: TUSKit.TUSAPIError.failedRequest(<NSHTTPURLResponse: 0x28347f300> { URL: <url> } { Status Code: 409, Headers {
    "Access-Control-Allow-Origin" =     (
        "*"
    );
    "Alt-Svc" =     (
        "h3=\":443\"; ma=86400"
    );
    "Content-Length" =     (
        23
    );
    Date =     (
        "Wed, 31 May 2023 16:14:12 GMT"
    );
    Server =     (
        cloudflare
    );
    "Strict-Transport-Security" =     (
        "max-age=2592000; includeSubDomains"
    );
    Vary =     (
        "Accept-Encoding"
    );
    "access-control-expose-headers" =     (
        "Authorization, Content-Type, Location, Tus-Extension, Tus-Max-Size, Tus-Resumable, Tus-Version, Upload-Concat, Upload-Defer-Length, Upload-Length, Upload-Metadata, Upload-Offset, X-HTTP-Method-Override, X-Requested-With, X-Forwarded-Host, X-Forwarded-Proto, Forwarded, Upload-Expires"
    );
    "cf-cache-status" =     (
        DYNAMIC
    );
    "cf-ray" =     (
        "7d0082268c553344-EWR"
    );
    "sb-gateway-mode" =     (
        direct
    );
    "sb-gateway-version" =     (
        1
    );
    "tus-resumable" =     (
        "1.0.0"
    );
} }))

Here's how I'm using TUS:

let tusEndpoint = Environment.SUPABASE_URL.appendingPathComponent("storage/v1/upload/resumable")

self.tusClient = try TUSClient(
    server: tusEndpoint,
    sessionIdentifier: "media-upload-queue",
    chunkSize: 6 * 1024 * 1024
)

let context: [String : String] = {
  var context: [String : String] = [:]
  
  if let mimeType = self.mimeType(forFile: fileURL) {
      context["contentType"] = mimeType
  }
  
  context["bucketName"] = <bucketName
  context["objectName"] = <fileName>
  
  return context
}()

let headers: [String : String] = {
  var headers: [String : String] = [:]
  
  headers["authorization"] = "Bearer <token>"
  headers["x-upsert"] = "true"
  
  return headers
}()

try self.tusClient.uploadFileAt(
  filePath: fileURL,
  customHeaders: headers,
  context: context
)

Start with the TUSKit.TUSAPI upload method and the Supabase resumable-upload endpoint shown in the report. Reproduce the large-file upload while repeatedly backgrounding and foregrounding the phone, inspect the raw 409 response and Upload-Offset values, and determine whether the conflict originates in TUSKit usage or Supabase's implementation.