That's interesting. I've heard another person tell me that as he has lost weight, he goes repeatedly through stages where his fat will first get "jiggly" before firming at a lower volume. I think I've seen it on myself, too, but I don't have high confidence. I've never heard this anywhere else before now. I'm wondering whether and how the hardness you are experiencing correlates with your size and weight changes, and with the carbohydrate content of what your eating. Have you noticed?

Edited to add: Okay, here's what Lyle McDonald has to say about it from Of Whooshes and Squishy Fat:

Many people have noted that fat loss is often discontinuous, that is it often happens in stops and starts. So you’ll be dieting and dieting and doing everything correctly with nothing to show for it. Then, boom, almost overnight, you drop 4 pounds and look leaner.

What’s going on? Back during my college days, one of my professors threw out the idea that after fat cells had been emptied of stored triglyceride, they would temporarily refill with water (glycerol attracts water, which might be part of the mechanism). So there would be no immediate change in size, body weight or appearance. Then, after some time frame, the water would get dropped, the fat cells would shrink. A weird way of looking at it might be that the fat loss suddenly becomes ‘apparent’. That is, the fat was emptied and burned off days or weeks ago but until the water is dropped, nothing appears to have happened.

For nearly 20 years I looked for research to support this, I was never sure if it was based on something from the 50’s or he just pulled it out of thin air as an explanation. Recently, one paper did suggest that visceral fat can fill up with water after massive weight loss but that’s about it.

Somewhat circumstantially, people using Bioimpedance body fat scales (which use hydration to estimate body fat levels) have noted that body fat appears to go up right before a big drop. This implicates water balance as the issue here.

As well, women, who have more problems with water retention, seem to have bigger issues with stalls and whooshes than men. Further, some individuals who have done dry carb-loads (high carbohydrate refeeds without drinking a lot of water) have seen them occur; presumably the body pulls water into the muscles and out of other tissues (fat cells). In lean individuals, appearance is often drastically improved with this approach, it doesn’t do much for those carrying a lot of fat.

...

I’d also note that this isn’t universal, lean dieters often see visual improvements on a day to day basis; a lot seems to depend on whether or not they tend to retain water in general. Folks who do have problems with water retention tend to have stalls and whooshes, those who don’t show nice consistent visual changes.

On a related topic, I wanted to discuss something else that often happens when people are getting very lean and dealing with stubborn body fat: the fat gets squishy, feeling almost like there are small marbles under the skin. Yes, very scientific, I know. That’s the best I can do.

As folks get very lean, down to the last pounds of fat, the skin and fat cells that are left will often change appearance and texture. It will look dimply (as the fat cells which are supporting the skin shrink and the skin isn’t supported) and feel squishy to the touch. This is bad in that it looks really weird, but it’s good because it means that the fat is going away. I have nothing truly profound to say about this topic, just realizes that it happens and usually indicates good things are happening.