Clockwise may think you already scheduled a lunch
Clockwise will recognize certain keywords to inform whether Lunch should be synced that day. If you have a meeting on your calendar with words "Lunch" in it, Clockwise will assume you manually scheduled your lunch block and will not create a duplicate hold.
You may be looking too far in the future
Clockwise optimizes your schedule for the current week, and the following 2 weeks (3 weeks total). If you're looking more than 2 weeks in the future, you won't see lunches scheduled.
Clockwise may think you're out of office
Clockwise recognizes events that indicate you're out of office, and will not schedule a lunch on these days. Scan your calendar to see if there are any such events. You can either decline an invitation to a colleague's out of office event, or update the category.
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