What happens if a session is missed? Can single sessions be cancelled?

The program isn't billed per session, so there are no single-session cancellations, refunds or credits - the fixed weekly fee covers the whole staffed program regardless of attendance. That said, let the coach team know as early as possible when a session will be missed: where practicable, CRANK will offer a make-up session (subject to availability, staffing and the participant's schedule). Group sessions are drop-in, so there's nothing to cancel. If whole weeks will be missed, use a pause instead.