We recently updated our Pipeline: Shared Groovy Libraries plugin from 2.8 to 2.13. As a side effect of upgrading, our retrieval method was wiped. We added the retrieval method again and set it to use GitHub and saved the configuration. Now every time we go back to the jenkins configuration screen, without modifying the Global Pipeline Libraries, the retrieval method is gone. So if someone were to change a different setting entirely, It would get rid of the retrieval method that was set causing issues to our jobs that depend on these shared libraries.
I attached a screenshot of what the retrieval method looks like every time on the configuration screen no matter if the retrieval method has been set and saved before.