Hi and hello this being your first post.
The volume that you hear depends upon a number of factors including the programme material that you are playing and the settings that you have chosen in Bartok.
We need to know a bit more about what you are doing to try to help.
Are you using Bartok directly into a power amp or does it feed a preamp?
Do you have Bartok with headphone amp and if so does your issue affect headphone listening?
What volume setting is displayed by Bartok?
What line voltage out have you chosen to use?
Are you using Mosaic for replay?
You mention your issue affects streaming Spotify . Do you use other sources e.g. local files, internet radio, Tidal, Qobuz or Deezer etc ? If so do they suffer from the issue?
The software history resource on the dCS website does not show an update for Bartok . Of course that resource may need refreshing if this is a recent change. Unfortunately as a Vivaldi user myself I cannot easily verify it. Nevertheless dCS product firmware updates usually have version numbers in the form v.1.0.x or v.2.0.x etc. so the one you give looks a bit odd. Either from Mosaic or from Bartok’s front panel display please advise the version numbers of the software/firmware installed.