Appears to be salpingitis or caseous exudate. Caused by the inflammation/infection of the oviduct by either Mycoplasma gallisepticum or Escherichia coli. Antibiotics are used to alleviate the symptoms but don't eliminate the infection. Some antibiotics commonly used are, Erythromycin, Oxytetracycline and Spectinomycin administered in either the feed or drinking water.
Hens infected will lay shell less eggs, or in your case, caseous exudate and can have pieces of egg shell mixed in the exudate. Eventually they will cease laying altogether, as the symptoms progress it can lead to death, if the hen can not get rid of the exudate, the mass in the oviduct fills up the abdominal cavity and presses on the lungs causing respiratory failure.
Soaking in a warm Epsom salts bath may help to reduce some of the discomfort experinced by the hen.
I've had this happen to several of my pheasant hens through the years.