When you make changes in Meta Ads Manager, certain edits can cause the system to re-enter the learning phase. During this time, performance may be less stable, and costs can temporarily increase until the algorithm re-optimizes.
Adding a New Ad Set to a Campaign
No impact on other ad sets — existing ad sets will continue optimizing as usual.
The new ad set will begin its own learning phase.
Adding a New Ad to an Existing Ad Set
This is considered a significant edit by Meta.
The affected ad set will re-enter the learning phase.
Other ad sets in the campaign are not affected.
Quick Summary
New ad set → Safe. Existing ad sets keep optimizing.
New ad inside an ad set → Resets learning for that ad set only.
For more detailed guidance directly from Meta, visit the Business Help Centre below;