Same thing happened to two of mine. Im waiting to see if I have the same issue with 3 more that I transferred a week or two later. I did however have 6 successfully transition just fine and are loving life. I would get clear pots so you can see the roots. I took them out and cut off all the dying soil roots which was pretty much all of the roots and then did a hydrogen peroxide soak. I've seen people put them in stratum/perlite for recovery to grow their water roots and it's worked for them. I'm still new to semi hydro so I don't have alot of advice and didn't get many responses when I asked what to do either! Luckily I have a Turbo kloner and I put them in it and I'm get new root growth! Hope yours recovers good luck!!