Well. There is a possibility that you have more than 1 that has Salpingitis.
These are the "new" chickens correct?
If they are approximately the same age, then you don't really know their "history".
They could have a respiratory disease like Mycoplasma or Infectious Bronchitis - either of these are a cause of oviduct infection later on life. Another common cause would be E. Coli infection.
You need to try to figure out which ones are passing the lash eggs and treat them. Antibiotics can help if caught early, but usually if you are seeing lash material, then it can be quite advanced and that material at some point starts blocking the oviduct and accumulates. This can press upon the organs, block intestines, cause crop problems and eventually death.
I don't mean to sound so negative, but I believe that people need to understand what can happen. Do some reading up on Salpingitis. There are a lot of threads here on BYC.
https://the-chicken-chick.com/causes-of-lash-eggs-salpingitis-by/