I believe this could be a huge waste of brain cells. As well known, the US of A has one or two current foreign policy issues regarding China (see other thread), and recalled their ambassadors to advise them in person of whatever the company line may currently be. More than likely, it will be an information briefing on what NOT to say in public within foreign circles in the respective host nations, since none of these ambassadors are lifelong diplomats. I see it as a standard operating procedure, and nothing worth getting into a fret over. They were recalled, not pulled.
Discussing what should and should not be said does not require an in person meeting back in the USA.
The recall of an ambassador is a serious step. There is no standard operating procedure historically on this type of action. It is done to show extreme displeasure over the host country's actions
The recall of an ambassador is the step just before breaking off diplomatic relations with a country completely.