Decomposition of iron(III) acetate?
Iron(III) acetate will be stable under these conditions. According to this paper, thermal decomposition to iron oxide only starts at 423 K (150 °C). Heating iron and acetic acid together with an oxidation agent (oxygen from air or, like in your case, $\ce{H2O2}$) is actually a suitable way to prepare iron acetate dyes (source).