One of my 8 month old RI Red hens has been doing this. She and her two siblings (as in, same age & same source) have been on "Layena Plus Omega 3" from the start, so I doubt that there's a lack of calcium.
Four days ago she laid a "rubber egg," as in there was no shell but a thick membrane; the next day she was lethargic (and no egg); the next day she was "bright-eyed and bushy-tailed" (or so to speak ;-) ) and laid another "rubber egg", and the same again today. Curiously, the last two "rubber eggs" were under their nighttime perch & not in the nesting box.
I was thinking of egg peritonitis when she was acting sick, but I wouldn't expect her to appear so healthy again.
FWIW, I now suspect that she's been the one occasionally laying light-pigmented shells, but their quality was normal otherwise. I also occasionally have gotten double-yolk eggs... again, I wonder if they have been from this hen & her hormones are just a bit off (?)
What think, experts? will she ever lay normal eggs again? what can I do to help her out, if anything?