It always happens at the same moment yeah, I reproduced it in a super simple repo with a one line Dockerfile and the default fly.toml file generated by fly launch.
Here is the output:
? Select region: fra (Frankfurt, Germany)
Created app black-feather-457 in organization personal
Wrote config file fly.toml
? Would you like to set up a Postgresql database now? No
? Would you like to deploy now? Yes
Deploying black-feather-457
==> Validating app configuration
--> Validating app configuration done
Services
TCP 80/443 ⇢ 8080
Remote builder fly-builder-weathered-wildflower-2423 ready
==> Creating build context
--> Creating build context done
==> Building image with Docker
--> docker host: 20.10.12 linux x86_64
Sending build context to Docker daemon 13.04kB
[+] Building 0.8s (3/3) FINISHED
=> [internal] load remote build context 0.0s
=> copy /context / 0.0s
=> ERROR [internal] load metadata for docker.io/library/swift:5.6-focal 0.9s
------
> [internal] load metadata for docker.io/library/swift:5.6-focal:
------
Error error building: failed to solve with frontend dockerfile.v0: failed to create LLB definition: unexpected status code [manifests 5.6-focal]: 500 Internal Server Error