garfieldnfish, thank you so much for your response. I found my golden mystery snail a few days ago and it was dead. It fell into some boxes I had under my cabinet (of all places) and it was a goner. For anyone who has smelled a dead snail, ugh.... it's foul.
The two that climbed out have fully recovered and have doubled in size. I have since had 3 more try to commit suicide and one appears to have been found too late. It's hard to keep tabs because I was raising some juveniles I hatched out from eggs and there are about a dozen. Most of them are magenta, so I cannot decipher between them.
I don't know why these younger ones are committing suicide, but it's upsetting. They aren't even egg-laying age. They are/were the size of dimes and nickles. The tank they were in was covered with a lid, but there are open spaces for the filter and where the heater should go. I do not keep the tank heated because it maintains a nice steady temperature because I keep my house warm and cozy.
I have been moving the suicide survivors into a brand new 20 gallon long planted that I started a few weeks ago. Astonishingly, the snails that have been moved to this tank have doubled in size in the past couple weeks. I'm taking this as a hint that the once-suicidal snails are much happier in their own tank!
In the previous tank, I had four larger and older mystery snails that were almost the size of golf balls (now 3, since Goldie committed suicide and succeeded). I think maybe the older snails intimidated the younger snails and in result, stunted their growth and made them want to take their own life??? I know for sure it wasn't a shortage of food, but I overfeed the tank because I have pygmy corydoras, which are super duper shy and because I want my snails to all eat well.
I'm amazed how much the once-suicidal snails have grown in their new tank!!!! So once the latest two suicide-rescue snails I found today recover, I will be moving them to that new tank.
I love these mystery snails. They really fascinate me and I think they are absolutely beautiful. I'm currently looking for a couple olive/jade and dark purple ones, so if anyone knows of a reliable source, please send them my way. Mystery snails do appear to produce quite a bit of bio-waste, but they are such characters!