Lash eggs happen for a few reasons. The Shell Gland can be defective in young birds or infections of the Oviduct will cause lash eggs. Of course old age causes break downs in the system.
If the Shell Gland (uterus) is not functioning properly, the yolk may not leave on time and it sits there and cooks. When it passes out it's nearly hard boiled. I have found that hatchery or poorly overbred hens many times have bad shell glands or ovaries that release yolks too fast. So you get eggs with no shell, yolks laid off the roost bars at night and lash eggs. Old age can effect how well the Oviduct functions and as a hen ages, she may lay more of these. This being said, a malfunctioning shell gland may only occasionally pass a lash egg. If this is the case, I wouldn't worry about it.
Infections usually happen to younger birds, bacteria gets up into the Oviduct and as far back as the yolks. Many times you can't tell the bird is all that sick until the infection progresses. If a hen is passing lash eggs regularly, especially a young bird, she has an infection. I have had great success with Amoxicillin, it's attacks this type of infection fast.
How old is your bird? Is this the first time you have found one of these?
