Comment 4 for bug 1608054

GRUB_CMDLINE_LINUX="net.ifnames=0 biosdevname=0" -> is not recommended at all, and might be harmful.

Do you have persistent interface names udev .rules file generated? That alone should be sufficient as that locks the eth* names by macaddress. The problem is that there is no guarantee that same interface keeps the same eth number across reboots. If you do not have persistent-net-rules generated, please do so if you insist on using eth* names instead of stable device names.

We have discovered that race conditions exist in ifupdown with systemd as pid1 resulting in certain paragraphs not executed correctly under certain rare circumstances. It might be possible to mitigate them, for your particular case, by adding a few more dependencies between ifup@.service and netowkring.service units.

For general case, I can only recommend to stop using ifupdown and migrate to netplan/networkd based configuration which is more reliable. On the other hand it is declarative, rather than arbitrary/turning-complete ifupdown configuration format.

Nonetheless such a simple case of just static IP addresses should really ought to work without a hitch....