Vanilla planifolia black and transparent stem sections

[duckhntr]

I have a newly purchased vanilla planifolia. It’s a decent sized plant. When purchased it was in a soil mix. I repotted it and left the soil mix but used orchida bark to fill the remainder of the pot. A few of the aerial roots died back but a lot of them are still alive. It has four main stems with a lot of roots. One stem is turning black on the bottom, another has a black section and all four seem to have small sections (1/4”-1/2”) that are more transparent. It is in a greenhouse, temp is 68-80. Humidifier is set to 65% and right beside the plant. The plant is getting around 800-1200 fc of light. Overall the plant still looks good and many of the aerial roots are still good and growing but I don’t know what’s wrong with these black sections or what to do. On a side note, we have 7 other small (8-10”) vanilla planifolia vines planted the same way in the same place that all seem to be doing well. Please advise.