hey there growmie, sometimes when excess moisture is retained in the medium you get some kinda water mold that causes root problems that causes these symptoms. mostly it's due to the fact the medium gets compressed or something so it retains water better towards the middle of the pot which is unfortunately where the main root stem is gonna want to live. Fix is by breaking down the problem roots using a chelation agent like enzymes, beneficial bacteria , or humic acid. add this and the plant should fully recover in 10 days or so. Hope this helps ! 🚀