I bought four of these chairs two years ago for our new covered porch and the bistro table. Darling design perfect on our gray porch and never get sun or rain. Stack them up in the winter and push next to the interior wall. About a month ago the webbing started cracking badly on one and is now cracking on another. What has caused this? Is it heat, cold, or a combination of the two? For indoor/outdoor we are very disappointed.