What's your question? Ask

It is best to plant in spring or fall. This reduces the stress on new plantings.

The creamy, white flowers are the only color available in this tree.

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/japanese-lilac-information.htm

I would inspect the tree for signs of pests or markings on the leaves and bark.
See if there is a break in that branch.
Prune out the damaged branch either back to the main branch or to a healthy leaf node.

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/japanese-lilac-information.htm

It sounds like your tree is showing stress from the lack of water, though over watering can also cause similar signs on the tree.

During warm and dry conditions you should water your tree once a week. To check the soil moisture level you will need to dig down to about 8 to 10 inches in the soil around the tree and canopy. The soil should be moist but never soggy. You should be able to make a ball of soil that holds but opens up when placed back in the ground. It shouldn't drip water when squeezed.
The amount of water will depend on your soil type.

In the spring following blooming you can prune any branches that may have some die back.

If it is just a little bit of bark, then I wouldn't worry much as this can be normal. If you suspect a pest, then I would Try to identify the pest. If you could send us a photo of the damage it would better help to assist you.

I would chalk this up to being environmental. This is normal and not usually a cause for concern unless you are seeing other symptoms. This is most usually caused by really dry weather followed by really wet weather. Here is an article that will help: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bark-coming-off.htm

Japanese Lilac actually make the list of trees that produce minimal litter.

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/japanese-lilac-information.htm