need a lot more info than that but looking at your plants they do not seem fine and happy to me...On the good side maybe put a photo on this link sorry I could not be more positive than that ...
https://www.icmag.com/ic/showthread.php?t=276325&page=19
Look at bit over fed to me the ones that are still alive with a few other issues probably related to over feeding.
Not wanting to upset you but the others will probably follow the same path as the dead plant. They do not look happy.
The plant to the left looks like it's leaves are hurting as well.
Start by giving us the pH, temp, humidity, nutrient feedings, possible pest issues.
What about a picture of the other plants ASAP.