Here's my .02 for whatever it's worth and it's relative to whitetails as I'm not well studied on any other deer species... and will add I welcome being corrected if anyone thinks I'm off course.
Shedding is triggered as fall approaches, daylight begins decreasing, and testosterone levels increase with rut approaching. While fall and daylight levels would have bucks shedding at the same time, testosterone levels will vary from buck to buck and are impacted by things such as age, general health condition, and especially malformations and / or injuries to... uhmmmm... an especially *sensitive* area.
It's not unheard of for does to grow antlers (and often they stay in velvet) due to hormone imbalances, and bucks with cryptorchidism (testicles remain in the abdominal cavity / never descend into the scrotum) or bucks with injuries to their testicles often will have lower testosterone levels that impair shedding.
All the above shared, the deer in the photo you shared look healthy enough I bet it was just natural variation / maybe age based. I DO see some natural variation among the deer at my place I attribute to natural variation. I'll note some haven't shed while others have, and then by the next camera card pull I make they'll all have horns hardened. Happens every year.
Link below does pretty good job speaking in general to horn development and velvet shedding.
http://www.realtree.com/deer-hunting/ga ... t-shedding
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