I have an issue with Premiere Pro CC on my Macbook. System reboot does not help. Tried different clip formats, result is the same. Intro tutorial has the same issue.
Premiere Pro version: 12.1.1 build 10
CPU: 2,7 GHz Intel Core i7
Memory: 16 GB 2133 MHz LPDDR3
Graphics: Radeon Pro 455 2048 MB
Thank you, playing with this setting helped.
Actually it was set to Composite Video. I first selected Alpha, then back Composite Video, then restarted Program Monitor. This did the job.