Had similar issues recently.
Went through peroxide, bleach and finally Hypochlorus Acid.
Make sure you remove any roots that are not healthy. I started gently handling the roots at first. Finally realized I was leaving diseased roots in the pots. I ended up tugging on anything suspect. If the roots are not healthy, they will break off.
I posted about it here Ramping up after 20+ years - #151 by JOHN1234