Hi,
common cause also wrong time zone settings on client or server. For example:
on server you have EET time zone (GMT+2), and on client you set it to CET (which is GMT+1). If you set clock on both server and client to be visually equal, they will in fact differ:
8:00 on server will be 6:00 UTC (because EET is 2 hours ahead of GMT).
8:00 on client will be 7:00 UTC (because CET is 1 hour ahead of GMT).
As system internaly uses only UTC time, when your client will request last hour data it will request 6:00 UTC to 7:00 UTC, but because on server it's only 6:00 UTC, you won't get any data.
Best regards,
Victor