I can't give definitive answers for why you are seeing what you are, with respect to Playlists not moving between the two installations. Part of the reason for that is that I don't understand exactly what MC does internally to manage Playlists, and I have never seen it properly explained. Maybe the authors of the tools like "Swag of Tools" and "MCUtils" know how it works and could explain.
First, let's get definitions on the table:Media Files: Means the music, video, and image files that you want to manage.
These are not your Library.
MC Library: Means the files that index all your Media Files. The default location for a MC Library is "C:\Users\<user name>\AppData\Roaming\J River\Media Center <version>\Library", and it consists of mostly *.jmd files.
There is a file called "playlistx.jmd" in the Library, and if that is being synced then I suspect you should be getting Playlists transfer. Matt confirmed that is where the Playlists are being stored, but whether that means just the name, or more, I don't know. Ref:
https://yabb.jriver.com/interact/index.php/topic,121874.msg843171.html#msg843171So, if you are syncing the *.jmd files from one PC to the other, then playlists should transfer. You can't just copy the "playlistx.jmd" between PCs and expect MC to keep working correctly. A Library is one internally consistent set of files and can't be mixed and matched. Well, not unless you
really know what you are doing.
If your home office PC is the only place you do maintenance on the MC Library, then what you should do is backup the Library on that PC and Restore the Library on the HTPC. If you are currently syncing the Library (*.jmd etc.) files, using a Library Backup would be far more reliable. However, both methods have downsides, as the HTPC Library will be updating "Number of Plays", "Bookmarks" and other similar tags, which you will lose if you overwrite the HTPC Library with either a Library Restore or Library sync from the Cloud. But you will get your Playlists to move from the Office PC to the HTPC.
Now, what I have read that other people have done in your situation, and possibly what you are actually doing, is sync the actual
Media Files (or perhaps more correctly, the directories in which the Media Files reside, which then includes Sidecar files, Cover Art, and other files in the directories) from one PC to the cloud and back to another PC. In addition, for tags of interest, they make sure that MC on each PC saves tags to the files themselves. In that way and tags created and saved on your office PC would be saved to the media files, which are synced to the cloud and back to the HTPC, and then the HTPC will note the change and update its Library with the new tags. I suspect that is what you are doing. I have seen some threads where people are doing that. It is not a foolproof solution, because not all tags can be saved to files, and if tags are only saved to a Sidecar file, I don't think MC picks up the changes.
When people sync their Media Files the way I have described, they have acknowledged that they need to export their Playlists from the source PC and import those Playlists into the target PC. That is the workaround for the Playlist issue.
Perhaps find references to what other people are doing and share them, to compare to what you are doing.
Note that if you look in the MC Options at Library fields, and display hidden fields, you will see that there are a number of Playlist related fields: [Playlist Name], [Playlist Description], [Playlist Guid], [Playlist Image], and [Playlist Type]. If you try to add any of those fields to a View, which you can only do using an expression because they are hidden, no content shows. However, while there is no [Playlists] field in MC, you can add a "Playlists" column to a View, and it will show the Playlists associated with a file. Neat, but confusing. You can't edit the contents of that column, showing that it is some type of special situation.
The better way to do what you want is to use MC's Client/Server configuration, with your office PC running as a MC Server, and your HTPC running as a MC Client. Then just back up to the Cloud both your Media Files and backups of your MC Library. But I assume that you didn't want to do that, because your office PC would have to be running to enable your HTPC to work.
Finally, MC wasn't built to be a Cloud-based application. Apple Music was. Even products that are supposed to synchronise to external databases, like Microsoft Outlook for example, have had a lot of trouble moving to being a Cloud-based solution. In fact in that case Microsoft pretty much rebuilt Outlook on a Cloud platform, rather than update the existing application. So, you can't really expect MC to do real-time synchronisation of Playlists given its development history. That just isn't what MC is. Of course, you could script regular Playlist exports, syncs, and imports, but that is out of scope for here.