LAN interfaces - high latency, low speed

[GreenMatter]

OPNsense (22.7.9) runs in VM (8GB RAM, 4 Intel Xeon E-2278G cores) with GB Intel NICs as vmx (virtual interface, full duplex). It's been all ok so far but I've just noticed serious problem in my network.
Everything what goes through opnsense LAN interfaces has high latency (over 1000ms) and speed between 2 and 10 Mb/s.
Speedtest run on opnsense to WAN is ok. Communication between switch clients (in the same subnet) is also not affected. Only when client hits OPNsesne LAN interface (to other subnet or WAN) speed goes down and latency is high.
What could be a reason, how to troubleshoot it?

[GreenMatter]

As I couldn't find any cause for such behavior I run:

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pkg upgrade -fTo my surprise nginx was downgraded:

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Installed packages to be DOWNGRADED:
nginx: 1.22.1_1,3 -> 1.22.0_7,3 [OPNsense]
Seemingly after reboot nothing was changed (as side note, previously till 5-10 minutes after reboot was ok and after that issue reappeared). But after next hour or so, problem disappeared. So, I'm lost when it comes to root cause of such network degradation...