MAM synchronization in some cases is done partially - only first page of the results is fetched.
Andrzej Wójcik (Tigase) commented 4 years ago
If the XMPP entity answers on the MAM request with <iq/> without complete in a <fin/> element and without count in <rsm/> then MAM sync is terminated.
If there is no count then we should check if first is equal last in the <rsm/> or if both are missing (first element equals last or no results).
MAM synchronization in some cases is done partially - only first page of the results is fetched.