I had a female two years ago prolapse an oviduct. My vet (it's my wife) was at a work-related conference in Spain or France, so I couldn't get with her immediately. It was prolapsed out about 10". I sent my wife an email, and decided I was going to do pretty much what I knew she was going to tell me to do THAT evening if she hadn't got back to me yet. She did, and I went out to take care of the situation. (Oh, relax - I wasn't going to "give her the pink juice.")
Here is the kicker, though. She had lost the prolapsed oviduct on her own. She looked normal. There was NO way she could have brought it back internal, so I dug around in the wet sphagnum she was in (she prolapsed after laying her eggs) and look HARD. I found the oviduct. It just looked like a thin piece of tissue, but it was so covered in sphagnum moss at this point that I would have NEVER seen it if I wouldn't have looked good. It made me wonder how often this happens and a keeper never even notices. If I would have waited another 36 hours to collect the eggs, I would have never known.
Anyway, I didn't breed her last year, but she ovulated in the other side this year. I got REAL curious. I threw a male in with her, they bred, and she dropped slugs over a period of ~10 days after her following shed. No re-breeding, but she tried to double clutch recently. She dropped 3 or 4 slugs and a mass exactly like you posted. Not as much of it, but exactly like that. Old female, but I'm pretty sure the remaining oviduct just wasn't working correctly. Mine was pretty gelatinous - no obvious yolk, albumin, or fertilize "spot." Of course, EVERYTHING she produced this year were slugs.
Obviously, this may be unrelated to what you found.
KJ