My 10 months son eats everything except porridge but for the past four months he's been weighing the same.The nurses are complaining but I don't know
And triple it by age 1 so he is expected to weigh averagely 11.7kg by 1 year.

Not eating porridge is not the problem but you need to ensure he eats balanced and healthy meals and also feed on demand.
Your baby's weight is okay as it is still within 80% - 120% of ideal weight range but it is important to make sure your baby's weight do not remain static or same or even worse drop below what it was before, those are very bad signs.
Kindly note that your baby is suppose to double his birth weight by 6 months