There is a new bug fix for the ethernet driver, just been merged to our github kernel tree on 4.14. This fixes a race condition that a couple of community member and PhilE of RPF(T) figured out. It may well explain a lot of the ethernet crashes reported by people on the 3b+, especially when using USB attached drives, or Samba, or things like Plex server.
It should be in rpi-update tomorrow, but in the meantime, you can build it yourself from here.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed.
I've been saying "Mucho" to my Spanish friend a lot more lately. It means a lot to him.