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Yellowing leaves generally indicate a watering issue, to much or to little.
Container plants need daily water and even twice daily if the temperatures are above 85 degrees.

Check the water and if the top inch or so is dry, water.
Soil should be damp and not soggy.
Make sure the pot is well draining.

These are fast growing plants and they may have outgrown your containers.

They also will not tolerate wet roots and can die from root rot very quickly.
Check the soil.

Certainly pests or disease are also a possibility, so inspect the plant and soil for signs.
I do think this shrub would be best planted out into the ground.

It is just most likely that the higher level of sun sort of blanches that section of the ceanothus. Sunlight is something we have very little control of in these circumstances. You could try a nitrogen fertilizer such as blood meal to green up the lighter side. This article may help
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/nitrogen-plant-fertilizer.htm

This plant is hardy in zone 8-10. It would not winter over in a cold climate.

https://www.gardeningknowhow.com/ornamental/shrubs/california-lilac/growing-california-lilac-plants.htm

Can you include a photo? This can help me to see the exact damage. Then I can give you a better set of care options. In the meantime, this article will give you information on their care: https://www.gardeningknowhow.com/ornamental/shrubs/ceanothus/caring-for-ceanothus-soapbush.htm

I recommend cutting the split branch all the way down. The large and extensive splitting is an open wound that invites pests and disease to "come on in". Give it TLC this summer and watch it come back. I hope BushDoctor also replies.