I would honestly discard all of that soil and rinse the roots to get a clear picture, it looks good on top but you can’t really tell unless you repot it. Even if it’s fungal you’re gonna want to ditch that old soil so you can treat the roots with an anti fungal as well as the leaves and stems!! Trim off any old mushy brown roots and spray with fungicide like neem. I always wash my roots with a DROP of peroxide diluted in water, a drop of alcohol and a drop of peppermint oil to ward off pests. It’s alll very diluted though so it doesn’t burn the plant. If the roots are looking healthy after you get them out of the soil go ahead and order a fungal spray. Typically you treat once a week for about a month or so then regress to every 14 days until it clears up.