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.
Your company may have reached their quota
If you are on the Free plan, your organization may have hit the limit for smart holds & schedule assists. You can either upgrade to the Pro plan, or wait until the next refresh of the limit cycle.
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.