Well, this is interesting, though not the first time strange things happen. As you have a custom build, it is difficult for me to make any tests on this. We have the plugin run aside multiple other plugins, though not the ones mentioned by you.
-First of some compile log would be nice. Maybe there are problems with duplicated class names or something similar.
-Also you can try to make a project with an official engine build and add the plugins there, see how it works out.