Dont know if u said or not but I assume your using an aerocloner..if so ive had tons of experience with these things, in fact i built my own years ago before they were even available. I deff had the same problems you had out of the blue..now one thing I know from experience is different stains will get soggy "melt" at different temps..most solid stains I use 80f exactly and never have a problem, then you might put a more unstable stain in and it melts in 4 days at 80f. Besides that, the number one thing I can recommend is to clean and run your cloner between every clone run, use a water and bleach solution..dont need much bleach just a cup maybe. Run for about 15-30 minutes with the bleach solution circulating in the cloner. Then dump it out, refill with clean water, run for a few mins then dump..refill with warm water and take your clones! Dont worry if theres still bubbles in the cloner from the bleach, this doesnt affect your rooting at all, ive actually left a bit of bleach water in the cloner and roots never looked better! You MUST do this religiously after every cycle or you will get the "melt".