The shrubs look pretty healthy overall, so this may be isolated physical damage from partially-broken stems, likely due to wet snow or ice. A stem that snaps, even if the break isn't complete enough for the twig to fall off, will damage the tissues in the wood that keeps the leaves hydrated, which is why they dry out and die. This partial breakage can be common on Japanese Holly and other shrubs with relatively stiff branching. All you need to do for now is to trim out these bleached/brown tips. If they recur, especially in the same general area, maybe a pet, child's toy, or something else is crashing into the shrubs from time to time.

The only other primary ailment Japanese Holly is notably vulnerable to which causes branch dieback is a disease called Black Root Rot / Thielaviopsis. Wet, poorly-drained soil with a higher pH (that is, nearly 7.0 or barely acidic) are the conditions which promote plant stress and opportunistic root infection. The fungus is fairly ubiquitous in our soils and it's not practical to try to eradicate it. Similarly, an active infection cannot be cured with a fungicide, though a hired certified pesticide applicator might have options for a fungicide soil drench which could protect uninfected roots. Even then, a weakened plant may not be able to recover well if dieback was extensive. A soil drench would be a measure of last resort, though it would be simpler to just replace the plants at that point.

To be clear, your plants do not appear to be showing symptoms of extensive dieback that this disease usually causes. We've mentioned this possibility, though, so you can keep it in mind if the dieback worsens, especially if the soil here tends to stay wetter for longer than it used to.

Miri