This a new one for me, but I actually haven't used pinhole cameras all that much. These observations were in Halifax, Nova Scotia, where there was about a 50% eclipse. With my 5x magnification pinhole telescope, I observed an obvious “speckle pattern”, which usually only is observed when projected by monochromatic sources of light such as lasers. The projection length was 80 cm long with a viewing length of 15 cm. The speckle pattern was obviously an artifact of the pinhole projection rather than the white card projection screen. As the camera angle was adjusted, the pattern was static within the disk of the sun's projected image rather than moving with the white card. I will have to experiment further to try to photograph the pattern.
"A speckle pattern is an intensity pattern produced by the mutual interference of a set of wavefronts" -- https://en.wikipedia.org/wiki/Speckle_pattern
Pinhole telescope apparatus seen here -
Solar Eclipse Halifax -