Well, I’m happy I found this thread, because I had a similar experience and I’m still busy playing with the decoupling of my system, I’ve been busy with it for a couple of weeks now, swapping various footers and trying to get the right balance between precision and musicality (much harder than I thought, by the way).
I’ve had the experience first with some AliExpress footers (3 ceramic balls pucks, ala "finite elements" without the price tag): I put them under an Ikea APTITLIG board, with my CD transport resting directly on the board. Not a good way of doing things but I was experimenting stuff. Anyways, from the moment those footers were under the board, the sound became open and wide but also lean with anemic bass. It was late that night and I decided to just go to bed and take them out the day after. But, to my surprise, when I played some music the day after the sound was much more "grounded", the bass was back (with a revenge!) but there was less bloom and openness. NOTHING ELSE had changed in the system, so I concluded that after a few hours, the footer settles in, maybe at microscopic level - the ceramic balls taking their final position, maybe, I don’t know, but it was very different.
Since that day I’ve been playing with a few different footers and I’m still busy with it, under my transport, under my preamp, I have a few different footers, some are soft and some are hard, and I have to say, it almost always changes (for better or worse) after a few hours of installation.
Now I must say, my system is a magnifying glass, every little change is heard big time, it has to play a part.