The most likely cause is the perspective has multiple groups/blocks containing rules that capture the same or similar tag values.
Any unique naming convention will be treated as a unique group. For instance, "environment" and "Environment" will appear as different group options. Repeat tag values are usually due to inconsistent tagging within your organization, so it's important to ensure you have alignment internally regarding tag naming conventions.
To avoid confusion within reporting, it is recommended to pull in all similar perspective groups and merging those groups or group blocks within the Perspectives Editor.