NetFlow Traffic Diagram WAN Interface monitoring crashes

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Hello there, I have searched the web for hours for the solution of a very strange issue I'm facing, to no avail.
Have a look of the following time-lapse of the Traffic Diagrams during three consecutive online speedtest runs:

During the first run, everything is normal (WAN In equals LAN Out), on the second run, the WAN Diagram line suddenly drops to 0 and stays there during the third run (only LAN Out shows a peak).
The only way to get the WAN Diagram line to show something else than 0 again, is to disable the VirtualIP it's connected to and enable it again. Then it works for a few seconds until it crashes again.
The issue persists on both of my firewalls which run the exact same configuration.

Setup: OPNsense 26.1.5 running as a VM on Proxmox 9.1.6 being connected by 3 virtual VirtIO NICs.

[Smash]

Currently it seems that I fixed it by fixing another upload related issue: https://lemmy.world/post/47842833

[nero355]

Currently it seems that I fixed it by fixing another upload related issue: https://lemmy.world/post/47842833

There are issues out there with certain Switches when they need to buffer traffic between 1 Gbps and 10 Gbps indeed, so that's always something to watch out for :)

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I wonder why a multi-gig switch isn't configured for this scenario by default though...

And the issue of this OP is back. The Traffic Graph worked for a while, but now WAN is missing again, really no idea why