You're right in that it isn't evaporation. If you do the math the leak rate is about 2.3 gallons per hour or a 55 gallon drum a day. If it's near the edge I would think you should see continual dampness but with all the rain you won't notice anything. Any chance the leak is outside the pool like in the external plumbing and you're not seeing it because of the rain? Don't have anything else to suggest at this time.
Al