AVPlayer seek completion handler not called

@AVFoundation Engineers, I get this bug repeatedly when using AVComposition & AVVideoComposition. Sometimes AVPlayer seek to time completion handler is not called. I check for a flag whether seek is in progress before placing another seek request. But if the completion handler is never invoked, all further seeks stall as flag remains true. What is a reliable way to know seek is not in progress before initiating another seek request.

      playerSeeking = true

        player.seek(to: time, toleranceBefore: .zero, toleranceAfter: .zero) { [weak self] completed 

            if !completed {
                NSLog("Seek not completed \(time.seconds)")
            }

            guard let self = self else {
                return
            }

            self.playerSeeking = false

            if self.player.rate == 0.0 {
                self.updateButtonStates()
            }
        }