thanks for the update - really irritating not having scrub!
let's all keep our fingers crossed
If you haven't already, please contact Synology support about this. The more people bug them about this (no pun intended), the more likely they are to get it fixed.
Also - if you really need the seek/locate function, you can get it by accessing your music through DS File. If I understand correctly, it uses iOS's built-in audio playback, which does have that functionality.
There are problems with this work-around: you can't use playlists in DS File, you can't see the name of the song that's playing, and if you don't recall exactly where a song is in your folders, you have to hunt around.
For example, a compilation album might be listed under 'compilations', or under 'various artists,' or even under the artist's name, depending on how it was tagged. I use my audio library for teaching music; on several occasions a song has popped into my mind which illustrates a musical concept, and I wasted precious lesson time hunting around in vain in DS File.