AVAudioEngine returning silence at the beginning of manual rendering

I am using AVAudioEngine to analyse some audio tracks and quite often the `while engine.manualRenderingSampleTime < sourceFile.length {` loop takes a moment to start receiving audio data. Looking at the soundwave looks like the input is simply delayed. This wouldn't be a problem if the length of the buffer would vary depending on this latency but the length unfortunately stays always the same, loosing the final part of the track.

I took the code from the official tutorial and this seems to happen regardless if I add an EQ effect or not. Actually looks like the two analysis (with or without EQ) done one after the other return the same anomaly.

    let format: AVAudioFormat = sourceFile.processingFormat
   
    let engine = AVAudioEngine()
    let player = AVAudioPlayerNode()
    engine.attach(player)
   
    if compress {
        let eq = AVAudioUnitEQ(numberOfBands: 2)
        engine.attach(eq)
        let lowPass = eq.bands[0]
        lowPass.filterType = .lowPass
        lowPass.frequency = 150.0
        lowPass.bypass = false
       
        let highPass = eq.bands[1]
        highPass.filterType = .highPass
        highPass.frequency = 100.0
        highPass.bypass = false
       
        engine.connect(player, to: eq, format: format)
        engine.connect(eq, to: engine.mainMixerNode, format: format)
    }else{
        engine.connect(player, to: engine.mainMixerNode, format: format)
    }
   
    do {
        let maxNumberOfFrames: AVAudioFrameCount = 4096
        try engine.enableManualRenderingMode(.offline, format: format, maximumFrameCount: maxNumberOfFrames)
    } catch {
        fatalError("Could not enable manual rendering mode, \(error)")
    }
   
    player.scheduleFile(sourceFile, at: nil)
   
    do {
        try engine.start()
        player.play()
    }catch{
        fatalError("Could not start engine, \(error)")
    }
   
    // buffer to which the engine will render the processed data
    let buffer: AVAudioPCMBuffer = AVAudioPCMBuffer(pcmFormat: engine.manualRenderingFormat, frameCapacity: engine.manualRenderingMaximumFrameCount)!
    //
    var pi = 0
    //
    while engine.manualRenderingSampleTime < sourceFile.length {
        do {
            let framesToRender = min(buffer.frameCapacity, AVAudioFrameCount(sourceFile.length - engine.manualRenderingSampleTime))
            let status = try engine.renderOffline(framesToRender, to: buffer)
            switch status {
            case .success:
                // data rendered successfully
                let flength = Int(buffer.frameLength)
                points.reserveCapacity(pi + flength)
               
                if let chans = buffer.floatChannelData?.pointee {
                    let left = chans.advanced(by: 0)
                    let right = chans.advanced(by: 1)
                    for b in 0..<flength {
                        let v:Float = max(abs(left[b]), abs(right[b]))
                        points.append(v)
                    }
                }
                pi += flength
               
            case .insufficientDataFromInputNode:
                // applicable only if using the input node as one of the sources
                break
               
            case .cannotDoInCurrentContext:
                // engine could not render in the current render call, retry in next iteration
                break
               
            case .error:
                // error occurred while rendering
                fatalError("render failed")
            }
        } catch {
            fatalError("render failed, \(error)")
        }
    }
   
    player.stop()
    engine.stop()

I thought it was perhaps a simulator issue, but also on the device is happening. Am I doing anything wrong? Thanks!