Premiere has never had very good support for audio and the user interface. Welcome to the channel linking rabbit hole.
Any audio engineer of any experience will recoil in shock when first introduced to the audio component. Adobe seems to be determined not to fix the mono/stereo problem. 20 years ago, Final Cut did this effortlessly, along with every other audio editing tool in existence. Fundamentally, audio tracks should present to the user as individual channels, linkable or isolatable at will of the editro. Instead, Adobe chooses to trap audio files in pairs, or assign in mono with the inability to link as pairs. Either, or. And, don’t get lulled into the whole “Audition” round turn technique either. Might as well learn to cut tape again with a razor blade.
So, my entry here is a complaint – I wish it were a solution instead. I gave up on doing serious audio work in Adobe long ago. Someone should post a workaround soon (which every time I learn to do convinces me that Premiere is useless for audio). You may have to re-import stuff and other nonsense, etc.
OK Adobe apologists, your turn.