Dave really sums it up. Not sure why your pool is dragging its tail on the OCLT, but it sounds as if you have been doing everything right. You have no drain, and I think you said before you had nicheness LED lights right? So that just leaves the pool shell (liner).
Without re-reading everything, I suspect this has been said before as well, but be patient and consistent. Start FC testing by grabbing the water sample from the same location, pump running to mix the water well, then using the same FC test process, etc. Hopefully you have a speed/smart stir to help you along. You mention the seams, so be sure there's not one or two of them folded down tightly that you haven't already exposed with a brush. We're rooting for you.