This issue contains of two parts:

1. Bug with late discovery of broken connection - fixed already in Tigase XMPP Server 5.3.0-SNAPSHOT

This issue caused broken connections to be closed only when packet was being sent, which delayed StreamManagement resumption activation

1. NPE in StreamManagementIOProcessor - fixed already in Tigase XMPP Server 5.3.0-SNAPSHOT

Due to this two issues presence packets sent from User2 to User1 caused broken connection to be discovered at this time and due to NPE in StreamManagementIOProcessor on start of resumption timeout resumption timeout was not initiated and connection was broken without StreamManagement. Next incoming message was bounced back by ClientConnectionManager as user connection was closed and in 5.2 version of Tigase XMPP Server it could not do anything else but to report error. (Error is defined if XMPP specification, not in XEP-0198).

As of Tigase XMPP Server 5.3.0-SNAPSHOT we have fixed both bugs so StreamManagement would work, but we also improved handling of messages to closed user connections in ClientConnectionManager which now sends them to offline message store.