Hi!
The global text has nothing to do with the font manager outline. This is probably some issue of compatibility with another plugin.
Take a look at the help file, there is a instruction for it to work with yanfly plugins. Follow it and see if it will work.
If still it did not work, we must find what is causing this. First step is download my sample project amd test the plugin there without the Global Text. If it works, them it is really a plugin from your project that is conflicting. Try find out what is, maybe if it is easy, I can provide a patch.