Common causes, in order of likelihood:

• Start Date or End Date empty/invalid - both are required; the clone silently does nothing otherwise.
• No kitchen selected under Select the Kitchens - every kitchen is skipped.
• No eligible dates in the range - dates must exist as delivery dates, be on the kitchen's fulfilment weekdays, and be open (not closed/finished, except for Catering).
• Source date is empty - cloning an empty day removes unordered meals from the targets and adds nothing.
• All source meals are disabled - inactive recipes are never copied.

Re-open the calendar and check the target month: green dots mean the clone landed.