I have a snake plant that goes back over 35 years, through multiple splits, re-potting etc. for the past couple of years, new leaves come in, looking normal, but then, instead of growing into wide flat leaves, turn into narrow, almost round stems, with just a slightly wider top. changing, light, heat, watering or re-potting don't seem to make a difference. What is wrong and how can I get it back to flourishing?
The leaves are drooping because they are top-heavy, with the wider part at the top and the very narrow bottom of the leaves. The older, broad leaves don't droop.
What is making the new leaves mal-form?
The ones in your photo all seem to be drooping, which in my experience means they could be weak from too much water and insufficient light. What are you growing them in? I'd suggest re-potting them firmly into some new fast-draining potting mix, formulated for cactus and succulents, available from your garden supplier. Discard any plants that look weak and stake the droopy ones up so they've got some support. Put your plant somewhere where there's plenty of light and warmth but not too much direct hot sun. Finally, give it a good soak and let all the water run out, but don't water it again until you can stick the top of your finger into the potting mix and it feels completely dry. The snake plant comes from the dry, rocky regions of the West African tropics so if you can make it think it's back home you will keep it happy!