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The JM roots were likely disturbed too much when the dusty miller was planted, and it also prevented oxygen getting to the roots and competed for water and nutrients. The best thing to apply under a tree is hardwood mulch out to the dripline.

It is ideal for cooler zones, but in your warm zone, afternoon shade would be helpful. It needs rich, moist soil.

Unfortunately, your photos did not come through. The genus, Acer contains numerous species, and some diseases are specific to species. A picture can help narrow down the species, or section.

Some Maples, like Sugar and Red maples will enjoy full sun. Some of the more sensitive Japanese maples will appreciate some shade. It could be that your species prefers one or the other.

Watering is another issue. Overwatering, or soils that do not dry out will promote rot and root suffocation.

Infections can be introduced to cause these symptoms, as well.

Many times, soils that have too much fertilizer will cause burning to trees as, as well.

Here are some articles that will help:

https://www.gardeningknowhow.com/ornamental/trees/maple/maple-tree-types.htm

https://www.gardeningknowhow.com/ornamental/trees/maple

Some possibilities for you to research:

* sunscorch occurs when the leaves are getting too much sun.

* underwatering (insert a finger into the soil and water if the soil feels dry; maintain the JM mulched up to the drip line).

* look for a pest infestation (aphids, scale)

I see a lot of green branches, which is good. They should leaf out either later/soon or in the spring. Hard to say about the leafless gray ones. Only you can evaluate if you want/need to return it or exchange it ( many places exchange instead of returning your money so check your warranty ). If you have branches with no leaves by late spring, prune those.

Is it getting any sun? It looks like it is on a porch. Also evaluate the watering. Let the soil dry out at the top before watering again.

https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maples-in-containers.htm