I upgraded today from 18.06.2 to 18.06.3 and I found out that kmod-igb and its dependencies (kmod-i2c-core, kmod-i2c-algo-bit, kmod-hwmon-core) are not in combined-ext4.img.gz for OpenWRT 18.06.3 x86/generic. Not sure if this was left out by accident, because it has been in every 18.06 x86 image up until now, and is a very common Intel NIC driver. However, because of it not being in there my NICs were not detected. My solution for now was to download and copy the IPKs for the driver and its dependencies manually over and install through opkg via USB.
(Moved to the For Developers section.)
Where you get 18.06.3 ? I have not seen 18.06.3 already build on the repos.
It appears to be now hidden or removed. It's not yet been released; and some who were able to download it have experienced issues.