There are several reports on the Plex Android apps user reviews of incompatibilities with older servers. Also that there are several requested features missing. While Serenity for Android doesn’t cover the remote control features and functionality yet. It does currently work with all known server versions.
Note this is primarily designed for Tablets and Google TV devices, it may work on newer phones, but isn’t optimized for those devices.
Serenity uses DLNA to discover your Plex Media Server and if for whatever reason it can’t find one, you have the option to enter the IP Address directly. Plex developers have said they are working on adding this feature but no time frame has been given. In addition, myPlex is not a requirement with Serenity. In fact it doesn’t support myPlex at all, as its primary purpose is to allow local access to your media.
If you are frustrated with the current Android plex client, then consider giving Serenity a try. If you don’t feel like buying it first, you can always try one of the developer versions for free from the project’s web site. Purchases through the play store help continue fund further development around the project.
The Plex developers will eventually get things straightened out, but you do have alternative choices to access your media your way.