Those faders are set to control cc7. They are not set to 0 in your screenshot they are set to “off”. There is a difference.
You said you have midi volume information in your tracks. That is why they snap back.
If you want to see a difference in how they work, delete your cc7 volume data from a track, then enable write automation on a track and record some fader movement.
As stated previously this is not the preferred way to control vst volume, but it will show you what these particular faders do.