Rendering Issue

Hi all, I've been mixing a track and have had issues rendering it for mastering. Once the audio is rendered and I play the file there are parts of music that are out of time, for example a kick drum. I've gone back to the project and listened through and everything is perfectly in time so it has to be something that's going wrong when I mixdown.. has anyone else experienced this? if so, what did you do to resolve this issue? Any help would be greatly appreciated, thanks

Rendering Issue