ASD and academic performance during the pandemic

My son has high functioning aspergers and has been a top set student for the past 3 years.   we received his timetable this week and without any warning he has been moved to set 2 with a reason that he has been outperformed by other students during lockdown.  my question to the forum is do i accept this or challenge the decision based on the additional pressure and anxiety the last year has presented to a teenager with aspergers ?   This is year 10 for him and a critical year for his GCSE’s.