GPUImageFramebuffer unlock crash on capturing "currentImage"

[CR34L]

If calling this method within a NSTimer the app is crashing with: Tried to overrelease a framebuffer, did you forget to call -useNextFrameForImageCapture before using -imageFromCurrentFramebuffer?
File: GPUImageFramebuffer.m, Line: 269

Code:
func createScreenShot() { DispatchQueue.main.async { if let screeny = self.session.currentImage { // do something else here self.currentScreen.image = screeny; } } }

May I missing something?