First, I'd like to say "Hello!" I have frequented this site a few times recently and it's been a huge help.
As you saw from the post title... I have a concern. I took a loathsome amount of time 4+ weeks to make sure my 20' dia. base (for 18' pool) was perfectly level, smooth, stone-less, and "soft" (Mason Sand under ground cloth/liner) and tamped both the ground AND the sand. Once I was comfortable/satisfied with the leveling (to within 1/4" of inch of variation from side-to-side), I then setup the pool - leveled vertically & laterally the legs checking them constantly while it was filling and let it fill overnight. The next morning the pool was within a foot of full, but I noticed 3 legs had "dropped" about 1 inch during the night. I thought, "I can handle 1 inch" - will drive me nuts aesthetically, but should be structurally sound, so I continued to fill. After about 2-3 days of fully filled I noticed the same legs (and two others) had dropped more wherein the original 3 legs were now nearing 2 inches low - this is a problem. HOWEVER, after hours of depth measurements around the actual pool floor - not the support legs, but the liner floor that the water is sitting on - I discovered the water itself is not out of level 1/8-1/4" of variation from side-to-side. It appears just the 3-4 frame posts/T's are lower than the rest of the frame due to settling.
That long explanation brings me to my question: Should I be concerned with the frame being "uneven" but the actual water weight and base is perfectly level (i.e. not sloping)? The frame structure "seems" strong - it has minor movement (not the legs, the upper horizontal ring) with water shifting during swimming play, but I attribute that to being normal. My yard is higher than either of my neighbors yards, so if something were to give way, then their yards and possessions would be likely "obliterated" from the water rush with gravity enhancement.
Would appreciate any feedback, advice, or musings on this before I attempt to jack the worst of the 3 supports if, for any reason, but piece of mind.