Error with :GFiles

- Category
- [x] Question
- [x] Bug
- [ ] Suggestion
- OS
- [x] Linux
- [ ] macOS
- [ ] Windows
- [ ] Etc.
- Vim
- [ ] Vim
- [x] Neovim

I'm encountering an odd problem, and don't know how to proceed. I've installed fzf with the following:
```
Plug 'junegunn/fzf', { 'dir': $HOME.'/.fzf', 'do': './install --all' }
Plug 'junegunn/fzf.vim'
```

Everything works correctly, except `:GFiles`. When I run `:GFiles` from a git repo, I get:

```
Error detected while processing function fzf#vim#gitfiles[6]..103_fzf[18]..fzf#run[64]..27_execute_term[73]..27_dopopd:
line 20:
E716: Key not present in Dictionary: dir
E15: Invalid expression: s:fzf_getcwd() ==# w:fzf_pushd.dir
Error detected while processing function fzf#vim#gitfiles:
line 6:
E171: Missing :endif
```

To make things more confusing, if I run the minimal vim configuration suggested here (`vim -Nu <(curl https://gist.githubusercontent.com/junegunn/6936bf79fedd3a079aeb1dd2f3c81ef5/raw)`, `:GFiles` then works. I have tried to replicated this by removing everything except the lines relating to fzf from my configuration, but still get the same error.

Any suggestion what to look at next would be appreciated!