The following happened to me with Vagrant 2.0 and VirtualBox 5.1.28, though I expect that it affects earlier versions of Vagrant, too.
When using DHCP with NFS, your initial vagrant up might like this:
[...]
==> default: Checking for guest additions in VM...
default: The guest additions on this VM do not match the installed version of
default: VirtualBox! In most cases this is fine, but in rare cases it can
default: prevent things such as shared folders from working properly. If you see
default: shared folder errors, please make sure the guest additions within the