Yaupon holly is tolerant of wide pH (5.5 - 7.5), and prefers a moist but not soggy soil. That being said, yaupon also tolerates occasional drought once established.

Nutrient deficiency may be at fault. Are the yellow leaves older or newer? Older leaf yellowing indicates a need for nitrogen, while younger leaf yellowing indicates a need for iron. Iron deficiency can cause nearly white coloration in some plants. Some nutrient deficiency is inherent to a particular soil and/or climate. For instance iron can be bound to alkaline soil. It's there but can't be accessed by the roots. The fix is to spray the plant with an iron chelate. Nitrogen and iron are the two most common deficiencies, but many other deficiencies can cause yellowing. Check out this LINK for a descriptive picture.

no evergreen holds its leaves forever ... interior leaves are shed as the canopy expands and shade them inside ...

the shedding is cyclical and can be be variable.. based on any stresses caused during the leafs life cycle ....

in other words.. it might be entirely normal ... and yes.. different plants in the same yard can react differently .... for a multitude of reason ...

please include your location in every post ... along with a history of at least the last year or two .... and in this case.. a pic or two might help us see the problem.. and help you ... use the camera/photo icon below the box you type in.. to add pix to a reply of this post ...

welcome to the forums ....

ken

If planted amongst other hollies showing no yellowing, it is likely not a nutrient deficiency nor normal leaf senescence. I'd question root development and expansion. A congested or compromised root system - often present at time of planting - will produce similar symptoms. Lack of a proper root system impacts the plant's ability to access both water and necessary soil nutrients. And this can be very individual to a single plant, affecting one but not affecting its neighbor.

But without any photos, this is all just speculation.....we are just guessing. And as ken mentioned, knowing a bit about the plants' history can help as well.