You posted a dmesg when you were running 5.7. At the time, your dmesg showed these em(4) devices:
Code:
em0 at pci1 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address 84:44:64:48:9f:49
em1 at pci2 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address 84:44:64:9b:20:54
em2 at pci3 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address 84:44:64:bd:90:d2
em3 at pci4 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address 84:44:64:79:0b:15
em4 at pci5 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address 84:44:64:70:4c:04
em5 at pci6 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address 84:44:64:b2:3a:3b
If the device numbers have been reassigned, you can determine this by comparing the MAC address numbers in your older dmesg with the MAC address numbers that appear in your 6.0 dmesg. If there is a real problem, you may circumvent it by reassigning the interfaces in /etc/hostname.* files and in /etc/pf.conf.
You may wish to report the problem to the OpenBSD Project. If so, please see
www.openbsd.org/report.html