I am author of SpaceVim. The main feature of spacevim is key binding guide. This feature need to run :map <prefix> to paser all mappings, and generate guide context. In vim, too many default key binding begin with g, most users include me do not remenber all of them. so I need the guide when I forgot next key after press g.
I think I can make a guess (but I have never seen this before either, and I haven't used SpaceVim yet) based on this issue: gq for reformatting doesn't work #787. nmap g [G] essentially blocks all the usual normal-mode commands that start g. gq, for example, is now [G]q.
nnoremap gf gf, by virtue of being a noremap version, blocks further mapping expansion, ...
I have exactly the same problem.
It seems that SpaceVim overrides the gf command in some way so that rails-vim plugin's gf doesn't check for _ on partial names anymore.
Also, you have to be on the partial name itself (instead of anywhere on the same line, thanks to vim-ruby plugin) for gf to work. So maybe it messes with vim-ruby too.