Hey y'all. I have these two "bubbles" that have popped up underneath my liner. My research says that this is generally due to water under the liner floating up. The wrinkles in the liner have been there as long as I remember, supposedly they didn't do the best job installing it. The wrinkles don't see. To be any worse, and have always been just a tight little fold.
These two spots are maybe an inch high at the tallest point of the bubble, not much. They have only appeared recently.
I hesitate to say this is a ground water issue, because nothing is floating in the deep end. We also have not had significant rain fall. Two years back we had a winter where it literally rained every day for months. There.was flooding everywhere and it was a muddy mess. We finished with much higher than average annual rainfall. That year and as far as I know forever this hasn't been an issue.
We did have a few days where we had a couple of significant individual rain storms that rained 3+ inches all at once, but that has been a week or two past and hardly any rain since.
I'm also puzzled as to why it has manifested itself in the center (ish) of the shallow end and not near one of the edges. Is it possible that a wrinkle or two somehow "combined" and the air contained in them is floating up?
I'm assuming no, since I always read that a floating liner is due to water.
Which brings me to wonder this. Since it's located in front of my steps somewhat, I sort of wonder if maybe the steps are leaking? I haven't done a bucket test, but I do plan to.
It might be in my head but also it seems to me that the liner is "looser" underfoot by the steps leading out that way. Maybe there is a leak where the liner meets the steps?
If it is water, what's the best plan of attack to try to suck it out way under there? I don't see me being able to fish any hose or tubing past the 90 degree turn and toward the middle right there.
If it doesn't get any worse, and it hasn't seemed to after a week or more, I don't know that I'm concerned about going to great lengths to remove it. We'll see.
I do have two spots where the liner is sagging maybe an inch low over maybe an 8 inch span, but they are waaaaay on the other end of the pool near the diving board.
Many thanks for any advice!
. When I step on it, it doesn't seem like there is a lot of resistance to my step behind it. It readily flattens out to the surface beneath the liner. 
. I topped it off and it doesn't seem to be dropping quicker than normal, and it doesn't seem that there is a leak with a bucket test. I'll maintain the elevated water level for a while and see if they come back. Those same spots don't look like a bubble any more, but they do have a big wrinkle sti that's been there a long, long time. 
