It seems that your plants experienced some stress around day 25, with some recovery by day 27, although one plant still appears to be struggling. Given the conditions you've described – appropriate temperature, stable PPM, firm and moist leaves, and no signs of root rot – the issue could be related to other factors like light stress, humidity fluctuations, or a minor nutrient imbalance. Since most plants recovered, it's likely that the environment is generally suitable. The one that's still struggling might have a slightly different sensitivity or could have experienced a localized issue. Keep monitoring closely, ensure consistent environmental conditions, and consider small adjustments to nutrients if needed.