I had that happen too recently… Basically rg x would show nothing but grep -r x showed the lines for any x. Tried multiple times with different x, then I kept using grep -r at that time. After a few days, I started using rg again and it worked fine but now I tend to use grep -r occasionally too to make sure.
I use "grep" to search files (it should never skip any unless I tell it to do otherwise) and "git grep" to be a programmer searching a codebase (where it should only look at code files unless I tell it to do otherwise). Two different hats.
I wouldn't want to use tools that straddle the two, unless they had a nice clear way of picking one or the other. ripgrep does have "--no-ignore", though I would prefer -a / --all (one could make their own with alias rga='rg --no-ignore')
Next time that happens try looking at the paths, adding a pair of -u, or running with --debug: by default rg will ignore files which are hidden (dotfiles) or excluded by ignore files (.gitignore, .ignore, …).
See https://github.com/BurntSushi/ripgrep/blob/master/GUIDE.md#a... for the details.