Oldest leaf dries up when new leaf grows

[Lilly B]

Three out of the four Phals that I have have started this season to have the oldest leaf wrinkle, dry up and fall off when the new leaf is growing. Plants all look healthy and one has put out a spike. All have healthy roots and I have not changed my watering pattern or amount of light they receive. I have had them for almost 7 years and it's heartbreaking to see the largest, oldest leaf disappear. I am posting a picture of one of them which now has 7 leaves left. She actually lost two leaves for one of the new ones last go round. The last photo is her keiki which is also loosing the olderst leaf with a new one growing. Any suggestions?