Looks to me like the hen's spray paint stopped/she decided to just drop the egg out (they can drop the egg out when startled even without much of a shell at all).
I have a RSL that lays a different egg every time. Some shaded, flashed,some freckles, lots of freckles, light ones dark ones, some with what looks like the paint ran. You could put her egg in with a 1000 others and I could pick it out.I should call her snowflake because there are as different as a snowflakes, no two alike. In her prime laying 5/6 a week this trend continued, she is 3 years old now and get about 2/3 and maybe 4 a week out of her. But still true to her "artisan" style. Most of my girls lay pretty uni-formally except a Buff Orp which lays an egg that is slightly deformed and not a perfect egg shape but true on color.