Issue while Implementing the Command Query and Responsibility Segregation (CQRS) pattern?

I would like to create a Proof of Concept (PoC) for CQRS Pattern.

If anyone has implemented CQRS pattern in an enterprise application or in a demo project, I would please like to know the following details.

1. What is the domain of the project? (Banking, Finance, Retail, Gaming, IoT etc)

2. What are the use cases addressed by the pattern in the project?

3. What issues and challenges did you face while implementing the CQRS pattern? [Important]

The issues and challenges part is important for my study. There are many cases in which CQRS is used with Event Sourcing (ES). It will also be of great help if the issues and challenges are related to the CQRS and ES pattern together.