Maybe I’m misunderstanding the API, but these two calls give me the same response (sorting by asc vs desc), so it seems like resolved_at doesn’t respect the sort_by:
curl -s -X GET --header 'Accept: application/vnd.pagerduty+json;version=2' --header 'Authorization: Token token=<TOKEN>' 'https://api.pagerduty.com/incidents?until=2018-08-30&offset=0&statuses%5B%5D=resolved&sort_by=resolved_at%3Aasc'
curl -s -X GET --header 'Accept: application/vnd.pagerduty+json;version=2' --header 'Authorization: Token token=<TOKEN>' 'https://api.pagerduty.com/incidents?until=2018-08-30&offset=0&statuses%5B%5D=resolved&sort_by=resolved_at%3Adesc'