Doesn't look to me like a root problem, the leaves are nice and firm. More likely either mechanical damage or the introduction of a pathogen from unclean water.
Question... do you soak it in water that has also had some other plant in it? If so, that's a good way to spread pathogens. I'd trim off that bad edge with a single-edge single use razor blade, (makes a clean cut, throw it away when you're done) and sprinkle the cut with cinnamon. Trim into clean tissue a bit, but don't overdo it, the plant needs leaf surface to photosynthesize. Keep the plant as separate as you can from other plants, and just keep an eye on it. if there is no further change in a few weeks, you're probably safe. Observation is one of the most valuable "tools" in your "tool set". The "time dimension" will tell you a lot. You can always increase the "treatment" if it keeps spreading, but if you cut too much you can't put it back.
(Still could be cold, too... it has been very warm during the day, but nights have dipped into the mid-50's F a few nights ago, if it was against a cold window that could do it too. I'm coastal, relatively temperate... inland or even a little more elevation, it could have gotten colder. This time of year the climate is extremely variable. Warm days and chilly nights, those Cymbidiums are gong to start spiking!)
Last edited by Roberta; 10-06-2023 at 09:45 PM..
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