I"ve grown Clivia for years and have only had one problem with blue/black hairy caterpillars. Now I have another problem. In one patch about 1m x 1m 5-6 Clivia"s were leaning over. When I reached in to straighten them up the green leaves and short stem came out of the ground intact, but without roots attached. It would seem that something is eating around the stem below ground level. I"ve used a Confidor drench and replanted, but I notice one of those is similarly affected. Any ideas, please?
I know the caterpillar problem - but total removal of the core of the plant as you describe suggests over watering to me. That seems like a big patch which might be prone to retaining water - but I bet they looked spectacular in bloom. Why not try separating them out - carefully - and see if that makes them more robust. I reckon they can be hardy. There was once a swathe of them at brisbane international airport that copped full western sun in the afternoon and they looked splendid. And I think I killed off some I had in a biggish pot that got too wet. Good luck.