The Learning Phase describes a period when Facebook’s systems are gathering sufficient data for effective ad optimization across targeting, timing, creative, and placement options. One of the most common topics involving the learning phase relates to making edits that reset learning.
An overview of the learning phase with best practices is available here, with a one-sheeter guide available here.
An article on our site related to the learning phase in general is available here.
An article related to edits during the learning phase is available here.