Theoretically, you have two choices to make folder rips work when using a PC as a MC Client.
1. Map a drive to the location where the Blu-ray folder exists, or use UNC Shares in your Library, so that MC can find the files as if they were local. You need to turn on the "Options > Media Network > Client Options > Play local file if one that matches Library Server file is found". Jmone has described this process a few times, and possibly in his network examples in the Wiki. Yeah, in Example 3, here:
https://wiki.jriver.com/index.php/Home_Networking_Examples2. Set the "Options > Media Network > Client Options > Video Conversion" to a suitable format for your MC Client. That is done on the Client, not the Server, usually. Unfortunately the choice to convert to haven't changed in some time, so 4K isn't on the list.
So it is the Client that tells the Server what to do.
Now, with JRemote2 I believe video conversions are always done. You have a choice in settings to select the video quality sent to the Client, being the Shield.
I just tested using JRemote2 on my Android phone, playing folder rips of Blu-ray movies, using the High quality video setting, and they all played without problem.
So does the Shield have quality settings in JRemote2, and have you tried them all?
I plan to install
JRemote2 JRiver for Android on my Sony TV shortly, if I can, so I guess I will see what options are available then. They should be the same as for your Shield.
EDIT:
Oh wait, this is for JRiver for Android TV, isn't it? My bad. I'll have a look at that now.