I'd really suspect sitbone width to saddle width is a major contributor to your distress.
If you could stand a huge gel saddle for 20-30 miles but then have big problems on a different saddle, I'd suspect width.
Lots of folks have problems from too much gel or cushion (because it compresses upwards) on the huge gel saddles and find them uncomfortable for the substantial rides you've done on it. Thick gel and cushion saddles often chafe and compress tissues worse than standard saddles. Loss of the gel is less likely in my mind to have caused this much trouble. What may be more likely is that you were weightbearing on your pelvic floor tissues and compressing the pudendal nerve and blood vessels and grinding the nose of the saddle into the softer bits, because the new saddle is narrower and maybe too narrow for the portion of your pelvis that contacts it.
Ideally you should be weightbearing on your sit bones. Sitting on a bike saddle with full weight on it (like, take your feet off the pedals) should be no more uncomfortable than sitting on a hard wooden chair.
You mentioned reading saddle posts already, so you've probably already found the saddle sizing threads. It really might be worth your time to do the various sizing tests. (BTW, hip width has very little correlation to ischial tuberosity width or pubic rami angle, so don't listen to bike shop boys who try to tell you what size you need just by looking at you.)
I have wide ischial tuberosities (in the 180mm range) and when I first got my Brooks B67 (210mm across the saddle cheeks) I nearly wept for joy over how incredibly unbelievably comfortable I was. Somewhere out there is the saddle for you, too! And you will probably feel that "aaaahhh" moment when you find it!
The right saddle is just as individual as the right pair of shoes. Sometimes it takes "trying on" several and a lot of trial and error. When you find the right saddle, buy 2 or 3 extra. Companies are notorious for changing designs.
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