Light randomly flashes when in the end. In later testing after I took a video, I noticed that it takes place anywhere on the main end island where the dragon spawns. I did not test the bug in the outer islands, However I would take a guess that it would happen there too.
Device: iPad Mini 6
Vibrant Visuals settings:
Shadow Quality: Low
Clouds: Medium
Reflections: Low
Bloom: 0%
Upscaling mode: Bilinear
Resolution: 75%
This issue is being tracked at MCPE-201557.