I imported a photo from my iOS library in Lightroom Mobile. Then I edited it on desktop (Lightroom only). I used B&W treatment with some basic adjustments, noise reduction, sharpening, gradients. After successful syncing I opened it on iOS device. Everything looked good. Saturation/Vibrance settings were disabled which made me think that it properly reflects desktop features. Unfortunately after saving image (to Photos app) or opening it (in Instagram) photo get magenta tint - definitely image had color information - it wasn't B&W. I found this issue with 2 out of 3 cases that had the same workflow.