Not sure if FlashChart is supposed to be enabled in WebServer Protection reporting but it isn't working. I can confirm the other ares where FlashChart is available is working fine on my machine.
On my UTM (currently v9.165-15) the graphs are all empty (0-values) because I did not have relevant traffic, but apart from that they are displayed correctly.
Are they not displayed at all in your case or showing wrong data? Or can you please attach a screenshot, if the situation is more complex?
Thanks,
Frank