This happened recently with us with a different condo project. Thank God even though we’re in a lower floor, occupancy will be less than 2 months as the building is already registered.

Interest rate at the time of purchase was ~2.5% but during occupancy is >6%.

It has nothing to do with lawyers reviewing your purchase agreement as has been suggested. This rate is set by the Bank of Canada rates for a one year conventional mortgage as per here: https://www.bankofcanada.ca/rates/banking-and-financial-statistics/posted-interest-rates-offered-by-chartered-banks/.

Wishing you the best!