I know I posted this reply in my other question, but I think it's more appropriate here:
Well, after a bunch of searching around on my system, I found a 2nd place where rc.inet1 is called. It's also called from /etc/hotplug/net.agent. And the only change I've made recently was to enable rc.hotplug so my USB ports are available at boot time for a UPS.
And guess what else I found. This in a SuSE sysconfig package changelog:
- is_iface_available(): It will now only modprobe <interface> if called from ifup, because it must not trigger unwanted hotplug events (#13178, dhcpcd was started twice)
Looks like Slack has the same bug.
As long as I can work out what that cryptic comment means.