Hello Ayaka! Seems like there was a known issue in the past three months and it was fixed for most meetings (MSFT ticket opened about theses issues: 120042424005380). It was resolved in Canadian zone last week, should be everywhere in a few weeks.
However, there's still a major improvement needed for other meetings. Dev team aswered us that "Falling back to SSS tracking. in telemetry for given Appointment. This is as designed behavior for such organizer. SSS tracking may take up to 30 min.” Can we get more votes for this to be improved?