Grafana - Empty CloudWatch logs queries

My CloudWatch logs queries are coming back completely empty. The queries work fine in the CloudWatch console, but even one as simple as the following returns nothing in Grafana. A whole lot of googling has turned nothing up. Does anyone know why this might happen?

stats count(*)
Metrics queries work fine from Grafana. The logs on the server don’t have anything at all. The request to /api/ds/query returns almost immediately with no data (data.values = []).

It was this issue. Per the discussion there, I restarted my service and it seems to be working again. I’ll see if it keeps working.