{"error":{"code":400,"message":"Unable to complete operation.","details":["Error executing tool.: Layer \"map_graphics\": ??\nERROR: code:400, , Invalid URL, Bad syntax in request.\nFailed to execute (Export Web Map).\nFailed to execute (Export Web Map Task)."]}}
This appears to still be an issue with API v3.20, after obtaining results from the Search widget (e.g., geocoding an address).
Wrote-up another incident: