How far away is your poller from the device being monitored? if I am reading the graph correctly you have a round-trip time of more than 2 seconds on occasion.
The default icmp ping timeout is 2500ms -- the command line ping may have a longer timeout (you have not included the output of ping so I can only guess as to what you are seeing).
You could increase this in the admin console (polling settings), but I would not.
Even the smallest site on the wa-K20 network, a server I know over 10000 miles away, or our research ship (RV Thomas G. Thompson) in the middle of the Pacific we don't see ping times that high!
I'd suggest looking at the network between your server and the things being pinged because something is not right with your network/host configuration, and this packet loss flag is just the canary you need to go and look at different issue (latency) rather than the ony you think you have (packet loss)