Activity Groups run at many different frequencies, some each week, some fortnightly, some at frequencies such as 1stTuesday of the month. Groups then take different approaches to breaks, for example not running during school holidays. Some groups such as Theatregoers have no set meeting times, as it depends on the Theatres' schedules.
While groups can specify breaks in their frequencies, this may not always be up to date, and the next meeting date shown could be incorrect. It is worthwhile being aware of your groups' policies for breaks.
There may be other causes for interruptions which are not under the control of the group - maintenance at the venue, elections, illness of the organiser.