frum cannot set local / global version

[s-p-b]

I'm not having any success with setting either a local or global version of frum. After going through the installation process detailed here, setting by .bashrc to initialize frum, and installing ruby 3.1.1, I try to set the global version, but still get the system ruby:

$ frum global 3.1.1
$ frum versions
  3.1.1
$ ruby -v
  ruby 2.3.7p456 (2018-03-28 revision 63024) [universal.x86_64-darwin17]

When trying to set the local version, I get this:

$ frum local 3.1.1
  error: We can't find the necessary environment variables to replace the Ruby version.

My machine is a mid-2009 Macbook Pro, running High Sierra 10.13.6
What am I doing wrong here? Thanks!

[nfgrep]

I had this happen aswell.
If I manually called eval "$(frum init)" immediately after calling frum local <version>, it would work.
I also noticed that this behaviour only happened when I didn't manually set the global ruby version with frum global.
After setting the global ruby version with frum global and then restarting my shell, everything seemed to work.
I suspect there's some logic that implicitly depends on there being a global ruby version.