The strawberry tree or Arbutus unedo is from the Mediterranean so it does not like lots of damp, wet soil. The only clue that it may be too wet is that you mentioned compost. Sometimes a thick layer of compost trap moisture and will encourage root disease. The yellow on the foliage could be a symptom of this. I suggest you pull back most of the compost and with the dry summer season coming up I suspect your tree will improve. It is a cute small tree not usually grown often enough so worth pampering a bit. It likes our naturally acid soil but does not need a lot of fertilizer. Keep growing, Marianne Binetti