Unexpected agenda changes often happen from new incidents, events or issues occurring between the Agenda being created and the meeting finally occuring. The key is to be able to weigh up the priorities of the new pieces against the prepared meeting goals. It's easy for even experienced players to get sidetracked in the mud of 'apparent urgency'. As the Facilitator, your role is to focus on achieving outcomes while managing the group dynamics. This includes analysing the importance of ad hoc elements and whether tackling them NOW is beneficial or a hindrance. By illuminating this to the group, the group can collectively define what needs to be resolved now, or tabled for another time. Virtual requires setting group rules to voice this well.