What's the impact on the CI job?
When the source of your CI job is a Git branch (e.g. a long-lived environment branch if you're using Pipelines feature), it's possible that the metadata you were expecting to be deployed is referenced in the .forceignore file within your Git repository.
A .forceignore or .gitignore file will tell git to ignore anything that is listed within it. If the component you're trying to deploy is referenced here, Gearset won't see it, and won't be able to deploy it.
How does a .forceignore or .gitignore work?
The .forceignore file structure mimics the .gitignore structure.
Each line in a .forceignore file specifies a pattern that corresponds to one or more files. The files represent metadata components - these can be any files you want to exclude from the deployment.
For more information about the structure of the .forceignore file, you can refer to Salesforce's documentation.
Also, you can refer to Git documentation to read about .gitignore.