The only thing I can think of is they are inviting applicants based on alphabetical order or of different countries of origin (like they have a cap for some countries within the span of time?). Again, I'm just speculating.. haha!
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/canadian-citizenship/ceremony/schedule/notifications-regarding.html
"
Preparing the list of candidates and the number of countries of origin
Citizenship staff should print the “Nominal Roll – Ceremony” form [CIT 0037], which is a list of the candidates for citizenship to whom a notice to appear has been sent, and make copies as required. The list should be sorted alphabetically by last name.
The nominal roll is used to check off the candidates’ names to confirm that
- they have arrived and submitted the “Permission Release and Consent”, on the last page of the “Notice to Appear – To Take the Oath of Citizenship” form [CIT 0024 CIF2] (see Allowing guests to take photographs);
- their Record of Landing documents have been updated and their PR cards have been collected.
The clerk of the ceremony will need to track the number of candidates’
countries of origin and provide the total number to the citizenship judge or volunteer presiding official. This information is available in the Global Case Management System (GCMS)."