Solved my problem. Turned out to be a leak at an elbow to a return on the opposite side of the pool than I thought. Apparently the water was working its way around the pool between the liner and formwork or behind the formwork and was showing up on the opposite side.

To find the leak I made a test rig consisting of a short pipe of 1-1/2 inch pipe (threaded in one end), a PVC coupling, and a two foot long piece of PVC pipe. I screwed thin into a return fitting and plugged the other fitting. I filled the standpipe with water and saw that it drained from the pipe in about 20 seconds. After letting it sit for a while I filled the pipe again and it did not take much water. That indicated that the leak was probably not far below the height of the fitting. I did this again on the other fitting and I could not add water fast enough to keep the pipe filled. I then dug down and over to expose this return pipe. My pool deck is only 3 feet wide so it was not real hard to do this. The soil on this side of the pool was hard and dry until I got very close to the pipe. I then put a hose against the return with the eyeball in place. I just held it there so that the pipes would not be pressurized to full water pressure. Although I had not completely exposed the pipe and elbow, water flowed down into the holes when I did this, so I am convinced that I found the problem. It is too cold to work with the liner this year, so I will fix it next spring.

Another point that may help someone. I had also suspected that the problem could have been at the underground fittings near the equipment slab since that slab has settled. I dug down to those fittings and exposed them. No problem there. If I had not found the leak I was considering cutting on the the return pipes there and installing a valve. Then I could have isolated the lines to see while one was the problem. I also thought about cutting the bottom off of a pool chemical bucket and burying this around the valve to provide future access.