Problem is, with perimenopause, my periods have lately been quite long. Current one is 2 weeks and showing no signs of stopping (don't worry I'm in touch with my doctor, he's not worried as it hasn't been consistently heavy). So I've been using my cup every day and most nights for 2 weeks. One day I forgot to dump/wash it when I went to bed so I probably had it in for 20 hours.
Anyway, it's the smell that's starting to be a problem. I'd dealt with this before and it's always righted itself without too much effort. I did used to use peroxide for stains (I know they don't recommend it, but the darn thing seems nearly indestructible). I've only boiled it occasionally. Have done so now, twice in fact, but of course that doesn't help. What stinky steam comes from the water, too, ugh! Soaked it in white vinegar (no change), then in warm water mixed with mild liquid hand detergent with baking soda (removed some stains, maybe a little of the smell). At present it's airing in my bedroom (away from cats but also from sunlight because there isn't any there, I put it under one of my remaining incandescent bulbs). Did a gentle, vinegar/water douche to clean things up below.
I think I'm going to buy another cup to rotate use. My sense of it is, as a long-term user who never had a real problem with odor, continuous use of the sort it's been getting may be the problem. It occurred to me that those using it for discharge, etc. might experience similar problems. Also I didn't see any other postings from women in perimenopause, so I thought I'd weigh in.