I’m booting from SD card on a KIII S905H rev c box that has 2GB of memory and typically has 1400MB free. I can’t tell you when this started for certain but I’d say it was in the last week or so. All I’ve done differently recently is mount a drive attached to my N2 upstairs into /storage. That said, this was done well before the onset of this problem.
I think I’ll install stable and check if the problem persists. If it doesn’t, then I’ll try each nightly until I find which one, if any, it is.
It might take me a few days to do this but I will post back.