Facing same issue mentioned in this post from 2014 but with Ardour 9.0.0 (Linux Mint 22.2). Certain vocal tracks are stuck on “implicit” solo mode, i.e. whenever I solo any other track in the project (even if they are totally unrelated, no routing or sidechain links to the “stuck” vocal tracks) , the vocal tracks get implicit soloed as well.
I’ve actually identified how to reproduce the issue for my session. The issue arises when I solo my vocal VCA (but not other VCAs for some reason).* Whenever I solo the vocals VCA, all upstream vocal tracks and busses get “stuck” on this implicit solo mode — this is shown in both mixer/editor by the green outline on the solo button and in the editor list by the shaded (but not filled) square under “S” column.
The fix I found is to click the “Solo” status indicator in top panel (above “Audition” and “Feedback” buttons). See the bug and fix in the gif below.
I’ve faced this issue for years in fact, I always thought it was caused by some hidden sidechain/routing link that I couldn’t find, but after I found the status indicator fix I thought it’s worth posting.
*FYI: My routing setup is: vocal recording tracks (mono) → vocal busses (main, harmony, adlibs) (stereo) → all vocal busses assigned to “Vocals” VCA.