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How much sun does this spot receive? This tree requires full sun to thrive. I also notice that it is planted very close to that building. Make sure that there are no water lines nearby. Roots can invade these causes quite a bit of damage. In some instances tree roots can cause structural damage as well.

Can you give me as much info about that spot that you can think of? This will help me to find out, exactly, what is going on here.

Failure to grow and leaf discoloration may be due to nutrient deficiencies. Soil and water management is the key. Fertilize with slow release organic fertilizer. Retain soil moisture and improve your soil with compost mulch.

Deep water every week during the hot season until the plant becomes established with a good root system.

If neem oil application helped, it may be suppressing a fungal disorder. But it's not a one time thing, it needs to be repeated every two weeks.

Yellowing leaves are likely due to plant stress and watering issues.
These articles will help you.

Make sure you are watering adequately.
https://www.gardeningknowhow.com/ornamental/trees/redbud/caring-for-redbud-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/watering-newly-planted-tree.htm

Redbud trees are susceptible to water deficit due to inadequate irrigation, soil nutrient difficiencies, pest and disease issues. It is impossibe to diagnose without more information on growing conditions and maintenance practices.
A local arborist or landscape consultant who specializes in plant health care can provide a site visit, diagnosis and treatment recommendations. Or a County/University horticulture extension service.

Trees require energy to sever the connection with leaves or other parts such as seed pods in fall/winter. When they are stressed, they are not able to drop leaves, etc. as they normally would.
The stressful period could have been late last summer to fall, or the tree could be in a general decline. There is no silver bullet for a stressed tree. Don't worry about removing the seed pods. Take steps to keep your tree as healthy as possible.
- Water during dry periods or droughts. Water deeply when you water. Do not drown it by keeping the water soggy all the time.
- Do not fertilize. Fertilizer is not medicine.
- Mulch a wide circle around the tree if possible. Do not ever pile mulch on the trunk. Keep mulch back a few inches. Also, keep mulch no deeper than 2-3".
Mulch helps keep the soil moist, keeps mowers away from the bark so it doesn't get damaged, and it also keep mowers from compacting soil over the root area of the tree.
https://www.gardeningknowhow.com/ornamental/trees/redbud/caring-for-redbud-trees.htm

Redbuds are tolerant of many conditions. These resilient trees will thrive almost anywhere, but in drier climates, it often needs as much water as you can give it. If you are concerned with its nutrient intake, you may feed with a higher nitrogen content fertilizer, as yellowing leaves is often a symptom of nitrogen deficiency. It is also helpful to add dolomitic lime to the area to keep the soil pH where it should be.