This is most likely flicker from the display or projector, not something physically blocking the screen.

Many screens and LED-lit displays control brightness by turning the light on and off very rapidly (PWM, or pulse-width modulation). Your phone camera’s shutter scans the image over a short period of time (rolling shutter), so if the screen’s light pulses don’t line up with that scan, part of the frame can record darker than the rest.

That’s why one image can show dark bands or uneven brightness, while the next shot looks perfectly normal. Slight zooming may also cause the camera to choose a different exposure/shutter timing, making the effect appear in one frame and not another.

This can happen with projector screens, LCDs, LED lighting, and some fluorescent/gas-discharge lights. It’s a timing mismatch between the light source and the camera, not a fault with your phone.

If it happens often, try taking another shot, changing the angle, or adjusting exposure if your camera app allows it.