The published list
Every edit affects delivery, but only a significant edit restarts learning. Meta names six that always do: any change to targeting, any change to ad creative, any change to the optimization event, adding a new ad to the ad set, pausing the ad set for 7 days or longer, and changing bid strategy.
Three more count only if the change is big enough: budget amount, bid control or cost per result or ROAS goal amount, and the ad set spending limit. Meta's own illustration is that moving a budget from $100 to $101 is unlikely to reset anything, while $100 to $1,000 may.
Why it decides whether an account ever stabilizes
The learning phase ends after roughly 50 optimization events in the week following the last significant edit, so the clock restarts with every one of these. Adding a single new ad restarts it for the whole ad set. Teams shipping fresh creative every few days, believing they are optimizing, are resetting learning faster than it can finish, which is how an ad set stays learning limited indefinitely. The full mechanic and the fix order are in the Meta learning phase guide.
Advantage+ campaign budget changes the blast radius
With Advantage+ campaign budget, switching the campaign bid strategy or adjusting the campaign budget can push multiple ad sets back into learning rather than one. Budget redistribution between ad sets does not, an ad-set-level edit does not affect its siblings, and adding a new ad set does not reset the existing ones.