swh-graph gRPC is particularly slow on Granet

Even something as simple as requesting an invalid SWHID, which shouldn't do any disk access, takes a few seconds:

$ time ./grpc_cli call granet.internal.softwareheritage.org:50091 swh.graph.TraversalService.GetNode 'swhid: "swh:1:cnt:zzzz" mask: {paths: ["swhid"]}'
connecting to granet.internal.softwareheritage.org:50091
Rpc failed with status code 3, error message: malformed SWHID: swh:1:cnt:zzzz
./grpc_cli call granet.internal.softwareheritage.org:50091    0.02s user 0.01s system 0% cpu 7.393 total