./scripts/env unable to create new environment

I am using multiple environments on my local master clone. When I try to add a new one, I'm seeing this weird message:

~/code/lede/master$ ./scripts/env new er4
Do you want to clone the current environment? (y/N): n
fatal: 'master' is not a commit and a branch 'er4' cannot be created from it
~/code/lede/master$ git branch
* master

A sanity check shows already plenty of environments:

~/code/lede/master$ ./scripts/env list
  amd64-unoptimised
  apu2
  ath79_generic
  ath79_tiny
  default
  fritz7362sl
  ipq40xx
* mt7621

Does anybody have an idea what's going on here? I tried an environment name without a digit, but no difference (besides, there's plenty including digits already there).

As a follow-up, I am able to create a new environment on a git clone without any pre-existing environments. I'm really interested in debugging this.

use set -x in env ... your output shows default... mine shows master...

how did default get there? rename?

These aren't branches, but environments. The branches are master, openwrt-19.07, and a local master-prep branch.

I found this meanwhile and I'l be trying a git fetch:

that could likely be the issue...