When creating an email subscription, users that were disabled using the Web Administrator User Manager still show up under the available users that can be selected as recipients. The issue is specific to disabling users from the Web User Manager. The issue does not occur when disabling users through the User Manager in Developer.
This is an identified issue in Strategy 10.x-2019 Update 1. This issue has been addressed in Strategy 2019 Update 2.
To resolve this issue, upgrade to Strategy Update 2.