While a matrix in a Jenkinsfile declarative pipeline with Docker agents seems to handle the executors per agent properly and provide each with a unique directory, the EC2 agents have trouble.  I have seen both shared working directories between matrix cells and multiple simultaneous executors on a single agent set to have only one executor.

The attached files come from the GitHub repo below and can be used to recreate the scenario in a local Docker setup.  A public AMI is provided but you will have to provide your own EC2 credentials and resources, of course.

https://github.com/altendky/jenkins-games/tree/295c50483d1bf01c8834e7dfdb7f9e0dec470468