Cinemachine playhead not working; recording not possible

I am attempting to record a scene with multiple instances of the Main Camera along a timeline, using Cinemachine and Unity Recorder. This worked with smaller clips but somehow the playhead no longer moves when pressing the play button. I can scrub along the timeline to see the camera transitions but not press play. Pressing play just jumps the playhead to a single camera position where it remains fixed; as opposed to transitioning to the next camera in the scene. This is an issue because pressing play is required to record and export the scene from Unity as a movie file. Any help is appreciated.

Forgot to mention, using a MacBook Pro 2014 running High Sierra with Unity v.2018.1.0f2 and was using this video as reference: Rendering Unity scenes as Video - YouTube