Hi… You can try --exclude-machines during deployment, which usually works around problems like this.
Apparently, there’s a known bug currently under scrutiny that’s causing some Machines to get wedged in an impossible state (replaced).
https://community.fly.io/t/machine-stuck-in-replaced-state/26648
If you have a support plan, you can probably ask for the zombie to be removed manually. (It’s best to use the actual Support channel to do so, though, rather than here in the community forum.)
Hope this helps a little!