Inconsistent PING behaviour on IP Camera

        I have just installed video system at 2 sites, Pelco VideoXpert Pro Server Version 3.12.0.79, with a few different IP camera models attached.

The model in question is the Spectra Pro P1220 PTZ Camera, there is 2 of these at one site and 1 at the other.
Like good network admins, we are running Network Monitoring Software (Paessler PRTG for anyone curious)

our PRTG Probe, which sends the ping, is sending it from a third remote server, VLAN tagged traffic via MPLS between the sites, and works fine with every single camera on the same subnet, except the Spectra Pro P1220 models, they do not respond to pings from this probe server.

AND ping -s (timestamp hops) works every single time, where ping with no parameters fails every single time.

Why does ping -s work, and not any other variant?

As i see it theres 2 possible scenarios,

• the Cameras CPU is too busy to respond (unlikely since timeout length doesnt make any difference, 4sec or 20sec it always times out)
• The network traffic somewhere along the connection is high enough that the routers drop ICMP packets (also unlikely since we are getting pings from 10 other cameras on the exact same connections)

I almost concluded that the cameras CPU is simply too busy to respond to ICMP packets, as i get a single ping through whenever i reboot the camera, and then it stops soon after fully booting.

However being able to ping from basicly any other subnet, and the fact that ping -s works from the PRTG subnet.

edit: words