I went for a run this evening, and based on the map, it looks like the GPS readings might have been slightly wrong. (It was a true out-and-back but doesn't show up that way.) We had some low, thick clouds today, so I'm thinking that might be a factor. Have you ever experienced this?
GPS is funny. Sometimes it gives really spurious results. But I looked at your route and the plot seems further off than I've ever seen. I don't think clouds would be the problem. Have you noticed this large of a discrepancy before? By the way, you can search "GPS accuracy" and find reams of comments and analysis.