I'm consistently able to reproduce this by upgrading Juju controllers on vSphere from 2.8.10 to 2.9.3. If I bootstrap with 2.9.3 then the problem does not occur.
Reproduction steps:
sudo snap refresh juju --channel 2.8/stable juju bootstrap vsphere sudo snap refresh juju --channel latest/stable juju upgrade-juju -m controller juju add-machine
I'm consistently able to reproduce this by upgrading Juju controllers on vSphere from 2.8.10 to 2.9.3. If I bootstrap with 2.9.3 then the problem does not occur.
Reproduction steps:
sudo snap refresh juju --channel 2.8/stable
juju bootstrap vsphere
sudo snap refresh juju --channel latest/stable
juju upgrade-juju -m controller
juju add-machine