Whats the soil that they are growing in like? How's the drainage? Are you fertilizing? How much water are they getting?

could you take some better pix.. not in blinding sun ... so we can see a bit better ...

dig the ded one out.. and find out what went on underground... did it grow out of the potting media.. put out ant roots into native soil.. etc ... [wouldnt be surprised if you cant just yank it out ... as i suspect root issues]

always add location also ...

how bad was winter ... out of the ordinary ...

ken

According to MoBot's PlantFinder "Wilt and root rot can be significant problems, particularly in hot and humid climates of the South. Susceptible to nematodes which can cause root rot."

Zone 7, east Tennessee. Mild winter, wet spring.

Here's what I've found so far.

1. Dead plant pulled out very easily. Large roots were broken about 1-1 1/2 inches below soil line, however the thicker roots did extend past the drip line. Finer roots were present on the plant. Soil was damp but not swamp-like (We had an inch of rain of few days ago).

No visible nematodes or other varmints present except for skink eggs. I know the eggs were recently laid because mama skink came back to cover the eggs.

Soil:

2. New photo of problem plant

Note the two-three stems/trunks in the ground. The foreground trunk has all dying leaves. The background two(?) trunks are mixed between healthy and dying leaves.

Same plant from SW side:

The flowers are growing off one stem/trunk.

Photoshopped for color. The black strip is electrical tape for color reference, white background. Right side is the dead/dying clipping and the left side is a clipping from the apparently healthy shrub.

Thanks, and let me know if this helps.