My company's platform is built on open source tech, a lot of which isn't mature yet, so we end up fixing bugs and adding features to it at our day job. Upstreaming them to the community is another story, and even when the code is finished and tested, things like backwards compatibility on old versions of the package and running on platforms you don't use can be a bear to support. It's definitely time consuming even when you can do the development at work.

My experience on other open source projects has also been when you put the work in to open a relevant PR and the maintainers just never respond to it. That's definitely frustrating.