The time in the oven is correct (20mins ) as is the temperature, never had his problem before, could it be oily almond meal? I need to make 6 batches for a wedding order and am now at my wits end.
So many possibilities. Yes, almond meal could be the issue, but I think it has more to due with environment. Think about how your kitchen felt when the macarons were "perfect". The temperature/humidity of a kitchen can have a drastic impact on the macarons' stability. Also, the egg whites' freshness and water retention can affect macarons' stability.
Thank you mr vittles, I usually bake with the aircon turned on and did the same these last few attempts, so I'm guessing it could be the eggs- maybe water retention as the eggs were fresh then age 24 hours.