By definition, "unsupported" channels lack the support of the greater channel development community. Each channel is usually written and maintained by a single individual. As such, the availability of support will vary greatly with the amount of time and energy the author has to devote.
Usually, the author will have started a thread in the Plex Channels forum. That is the best place to start looking for help. Often, known issues and possible solutions, as well as updates, will be discussed in the thread. Always review the first post of the thread, as that is where the developer will often include any updates, special instructions, or known restrictions on use. Reviewing or searching the thread will often reveal answers to frequently asked questions. If an issue is not covered in the relevant forum thread, then posting a question in the same thread is often the best way to catch the attention of the developer or other helpful users.
Related Page: Find my Plug-In here for support
For channels downloaded directly from GitHub, users can log in to GitHub and file bug reports directly for the channel repository.
It is not uncommon for channel developers to "disappear" or retire from channel development as other interests and responsibilities take priority. If the sole developer of an unsupported channel goes absent, the abandoned channel will generally fall into disrepair over time and stop working unless another developer takes over the maintenance.