Masdevallia strobelii with yellowing new growth

[greenbean]

I've had this Masdie since July of this year. It's been growing beautifully and still is, except for one new growth that has turned yellow. It's growing healthy new roots and has several other new growths besides this one that are as healthy as ever. I see no signs of fungus or bacteria. It's growing in New Zealand sphag in a tank with indirect natural light supplemented by a fluorescent tube. Temps are in the mid 70's during the day, mid to high 60's at night. RH around 80-95%

Any ideas as to why this one growth is dying?

I'm pretty sure the damage on the older leaf is purely physical/mechanical. It was like that when I got it.