Hi, I had this same problem too. Whenever I would update my details it would be "saving" for hours. If I updated the app description though it would save instantly.
After struggling for nearly a week, ironically enough I was preparing to record a video for Apple and during the screen recording, it saved! Give it a go, this was about 3-4 days ago so it might have been resolved a short while after you posted this
milad132
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Hey, it seems to be working for me now!
I also ONLY have this problem when I try to update the "App Review Information". I have no special characters elsewhere, and every other section has saved fine
same here!