[master < T963] Fix distinct, no longer impacts other aggregates

[Ignition]

Before a distinct on one aggregate would impact distinct on another aggregate. Fixed the logical error and at the same time did some memory optimisations.

[master < Task] PR

• Check, and update documentation if necessary
• Provide the full content or a guide for the final git message

To keep docs changelog up to date, one more thing to do:

• Write a release note here, including added/changed clauses --> "Fixed logical bug in distinct processing of multiple aggregates"
• Tag someone from docs team in the comments

closes #963