It took a bit of digging to find the reference on IRCC but this is known to many that applied before.
Do I (the sponsor) have to continue to meet the income requirements during the processing of the application?
If new information indicates that you may no longer meet the income requirements, your income may be reassessed at any time during processing. Your income could also be reassessed if more than 12 months have passed between the dates since we received your application and when processing of the application begins.
You and your co-signer, if applicable, must meet the income requirements outlined in the
Income for Parents and Grandparents Sponsorship from the date on which IRCC receives your sponsorship application until the day your family members become permanent residents of Canada.
It's at the middle of this guide. search for the wordings.
Guide 5772 – Application to Sponsor Parents and Grandparents - Canada.ca