Hi novalix.I found your mix a bit warm .actually this warmth is ready to transform to the muddiness.Lead vocal seems deep and low.
Mix needs some clarity and balance.
Back vocals need to control with compressor.(maybe you should control their reverb send with a compressor or automation-sometimes they're out of control.
If you ask what is the most important problem .
To me the clarity and low end control are so important to balance your mix .Hope that helps.
To solve it you should use more aphex vintage exciter(kidding
Mix needs some clarity and balance.
Back vocals need to control with compressor.(maybe you should control their reverb send with a compressor or automation-sometimes they're out of control.
If you ask what is the most important problem .
To me the clarity and low end control are so important to balance your mix .Hope that helps.
To solve it you should use more aphex vintage exciter(kidding
Little details always gives inspiration to change your perspective