Nomad 0.12.11 was released with a bug fix to avoid having new servers bootstrapping prematurely when configured with bootstrap_expect = 0.
We shipped the fix initially in Nomad 1.0.2 and have backported it to the Nomad 0.12 line.
Links:
Changelog - nomad/CHANGELOG.md at v0.12.11 · hashicorp/nomad · GitHub
Binaries - Nomad v0.12.11 Binaries