Yeah, as you thought: “no snap found” .
snap.log gives me the following:
2019/04/24 11:16:44.400804 helpers.go:229: DEBUG: Going to download snap "hello-world" (unset) from channel "" to "".
2019/04/24 11:16:44.401201 retry.go:41: DEBUG: Retrying https://api.snapcraft.io/v2/snaps/refresh, attempt 1, elapsed time=21.075µs
2019/04/24 11:16:44.401604 logger.go:67: DEBUG: > "POST /v2/snaps/refresh HTTP/1.1\r\nHost: api.snapcraft.io\r\nUser-Agent: snapd/2.38+18.04 (series 16; classic) snap elementary/5.0 (amd64) linux/4.15.0-47-generic\r\nContent-Length: 351\r\nAccept: application/json\r\nContent-Type: application/json\r\nSnap-Classic: true\r\nSnap-Device-Architecture: amd64\r\nSnap-Device-Series: 16\r\nSnap-Device-Store: LimeNET\r\nAccept-Encoding: gzip\r\n\r\n{\"context\":[],\"actions\":[{\"action\":\"download\",\"instance-key\":\"download-1\",\"name\":\"hello-world\",\"epoch\":null}],\"fields\":[\"architectures\",\"base\",\"confinement\",\"contact\",\"created-at\",\"description\",\"download\",\"epoch\",\"license\",\"name\",\"prices\",\"private\",\"publisher\",\"revision\",\"snap-id\",\"snap-yaml\",\"summary\",\"title\",\"type\",\"version\",\"media\",\"common-ids\"]}"
2019/04/24 11:16:44.666685 logger.go:74: DEBUG: < "HTTP/1.1 200 OK\r\nContent-Length: 247\r\nContent-Type: application/json\r\nDate: Wed, 24 Apr 2019 09:16:44 GMT\r\nServer: gunicorn/19.7.1\r\nSnap-Store-Version: 13\r\nX-Request-Id: 5D8590BD9CEA0A325C9601BB5CC0297C418E7110\r\nX-Vcs-Revision: fe3891e\r\nX-View-Name: snapdevicegw.webapi_refresh.snap_refresh\r\n\r\n{\"error-list\":[],\"results\":[{\"error\":{\"code\":\"name-not-found\",\"message\":\"The Snap with the given name was not found in the Store.\"},\"instance-key\":\"download-1\",\"name\":\"hello-world\",\"released-at\":null,\"result\":\"error\",\"snap\":null,\"snap-id\":null}]}\n"
2019/04/24 11:16:44.667266 retry.go:53: DEBUG: The retry loop for https://api.snapcraft.io/v2/snaps/refresh finished after 1 retries, elapsed time=266.065884ms, status: 200
error: cannot download snap "hello-world": snap not found