First, welcome to this forum. The soil mix you're using is too "heavy". That is to say, it will hold too much water over a long period of time. You want to add at least 50% perlite. Next, your humidity is usually high despite your high temps in the summer, so watch that you don't overwater. Can't tell you why it has lost the central leaves. but it is etiolated; small leaves/thin stem. The cause for this is usually insufficient sunlight, but don't put this out in full sun without a period of slow acclimation or it will sunburn. In time the head will get larger and the leaves will grow tighter together.

I agree; the potting mix is too heavy, particularly in that overlarge container (put it into a smaller pot), and the plant has shot up looking for light, I think.

Josh

Tis a sad one isn't it ???? Centre looks like it has rotted out and dried up as they can do. Definitely not in enough light, too big a pot and as previous posters had said soil isn't loose enough. Recovery will be a slow process. It has been a lowgrowing plant which offsets closely. The two stalks are offsets that haven't been given enough light so have stretched to try to find it.. Main plant will most likely not grow from the centre again. If I was dealing with it I would introduce the plant into early morning light for a week or so then to more direct light till about 11am till the little plants look firm and the rosette form tighter. Then I would cut them off dry the stems for a few days then replant into dry soil until roots appear. If you achieve this you will feel like " Mother Hen " Soil needs to be very open Enough that when you hold a slightly damp handful tight, then open your hand the soil breaks up. If it stays tight it needs more coarse sand, perlite etc. But in all honesty,it would be a long haul.. I would head for Collectors Corner or your nearest Nursery and buy another one. In Melbourne you can have them outside in good bright light most of the year, but a sheltered spot out of heavy rain. They are not happy inside, look O.K. for a few days, them colour fades out and plant elongates.