Why didn't IntervalCoach add a workout on a day that already has one?

IntervalCoach won't double-book your calendar. If a day already has a workout on it — one you added yourself, one from another plan, or a completed activity — IntervalCoach leaves it alone by default instead of stacking a second session on top.

What happens by default

When a day already has a workout, IntervalCoach doesn't generate a new structured one there. Instead it sends your daily status email noting the existing session (with fueling advice) and leaves your calendar untouched. This keeps it from overwriting sessions you or another plan put there.

If you want IntervalCoach to plan that day instead

Clear the slot first: delete the existing workout for that day in your Intervals.icu calendar, then let the daily email regenerate (or use JustTrain to create a session on demand). With the day empty, IntervalCoach will plan it.

Letting IntervalCoach adapt existing workouts in place

If you'd rather have IntervalCoach adjust the workouts already on your calendar, turn on Adapt External Workouts in Settings → Goals (under Daily Adaptation — it needs your weekly plan and daily adaptation enabled). With it on, IntervalCoach treats an existing workout like one of its own: if your readiness has changed enough to matter, it generates an adapted replacement for the day; if nothing significant changed, it keeps the original.

"My planned session isn't on my Intervals.icu calendar yet"

That's expected. Workouts are generated one day at a time, 7 days ahead — so a session further out lives on the Training Plan page first and only lands on your Intervals.icu calendar as its day approaches. You can preview and edit it on the Training Plan page in the meantime.