So the most blocks that are transparent or have 2d texture overlap.

On transparent blocks (glass block, glass pane, door, etc), the non-visible part is visible and gives a strange appearance. (seen on the pictures)

On 2d blocks (rails, iron bars, grass, etc), it flashes some black stripes (seen on the videos)

"How did it start happening?"
I don't know.

"When did it start happening?"
I think it started happening on the latest update, not sure.