hi Jaasperff
Are you using "prefer AMON over SNMP" in your Airwave ? If so, please make sure that your Airwave version is up to date, the same issue you have can be after an AOS upgrade if the Airwave version is too old to query the AMON schema from the controller.
This is due to a security fix that went into ArubaOS 6.3.1.5 which leaves older Airwave software unable to query the AMON schema from the controller. This results in flat graphs as you have seen. If you are on Airwave 7.x, make sure to update to the latest 7.7.x version, there should be no issue if this is AW8.x
Other causes of graph issues when using AMON (though not likely to manifest from an AOS upgrade, but just for completeness) are
a> firewall type device dropping fragemented UDP packets > 1500 bytes
b> firewall blocking controller -> AW comms for udp/8211
c> firewall blocking AW <> controller comms for tcp/4343
regards
-jeff