This is related to background/Declaration.It's because in the PGP checklist document it states that there should be no gaps in education.
Schedule A - Background/Declaration (IMM 5669)
IMPORTANT: For this form to be accepted, it must be complete (incuding no gaps in time for education and personal history in sections C and D)
As long as you MENTION the timeframe of the particular gap, It won't be an issue. IRCC wants to know each year's details. So if there is an education gap, just have to mention it or include that gap in one continues raw.