r338446: network access freezing on em/igb NICs

Running CURRENT (FreeBSD 12.0-ALPHA4 #19 r338446: Mon Sep  3 21:07:45
CEST 2018 amd64) on a PCengine APU2C4 (NIC is 3x Intel i210:
[...]
igb0_at_pci0:2:0:0:        class=0x020000 card=0x00008086 chip=0x157b8086
rev=0x03 hdr=0x00 vendor     = 'Intel Corporation'
    device     = 'I210 Gigabit Network Connection'
    class      = network
    subclass   = ethernet
    bar   [10] = type Memory, range 32, base 0xfe500000, size 131072,
enabled bar   [18] = type I/O Port, range 32, base 0x1000, size 32,
disabled bar   [1c] = type Memory, range 32, base 0xfe520000, size
16384, enabled
[...] )

When connecting to the as router acting APU from inside my SoHo network
from any machine or via serial console, there is no obvious problem so
far detectable. Using top(1), which is my indicator for the problem, is
sending normal output. The router has igb0 as tun0 and is spanning the
network via vlans via igb1. Connecting to a host inside my network and
havinf heavy net I/O doesn't reveal any problems so far. Direct access
to the APU from outside is prohobited.

When loggin into a host inside my private net from my department and
then from there toward the router (APU) as a wheel-grouped user also
doesn't reveal problems using top - but I have users restricted to see
only there own ID and also there groups are limited via some
bsd_see_others... sysctls. It gets funny when sudo su -'ing to root on
the APU and then using top. Immediately the net traffic freezes forever!

Kind regrads
oh