The screen has no formal default for the data such as series ID (that I can recall).
However, in your release, a “user” can create a template for data entry. In doing this you can begin to create a record, then save that as a template.
When creating a new record in the screen, you can optionally use the template such that data fills the screen.
If a user takes the next steps, you can assign a template as default. When a template is set as the default, then simply when creating a new record, that template is used.
I suspect this is what happened, and the CI is now defaulting based on a default template.
To remove the default template from being used see the below.