Some food is thawing in my chest freezer

I have a chest freezer Model # 253.11541100 I have had it in my garage since I have owned it. About 2 yrs ago I lost some meat as it alsmost thawed then refroze. I have kept an eye on it as it wasted about $250 of meat. This week it has done it again. Areas of the freezer are thawing the meat while the rest of the meat is kept frozen. Why does this happen? This time the meat was on the bottom and covered with frozen meat. My ground sausage, bologan and green pepers thawed half way. I am afraid it ruined my sausage again.

Why does this do this? Is there any recomendation?