When switching sources, picture may be lost while the source and display or sink boot and negotiate with each other.
HDCP requires verification of digital rights continuously, not just at initiation. Any break in this continuous verification may or will require a re-initialization or re-boot once that break exceeds 2 seconds or less. Unplugging and re-plugging an HDMI cable will cause this re-boot or the re-boot may happen automatically by the source and the sink after several seconds.