Getting Stuck at `Deployment is running pending automatic promotion` when trying to deploy.

Currently when running flyctl deploy on a project, I’m getting stuck at:

v19 is being deployed
v19 running - Deployment is running pending automatic promotion.

Looking at fly logs nothing has happened besides a message stating, long after the deployment:
2021-12-09T14:06:25.974 proxy[bbe9e672] nrt [error] Error 1: Undocumented.

Note: this is only happening after removing a mount from fly.toml.

is there a fix for this, is this a known issue?

Strangely, flyctl deploy --no-cache --strategy immediate worked to fix it.
Looks like something just got caught in the cache?