Propane should not evaporate from the tank. That would sure create a fire danger. Maybe a piping leak, might want to have it pressure tested. Have the propane supplier check all fittings on the tank with soapy water.
My neighbor is on auto fill and the propane truck seems to put more than a few gallons every month. I always prefer to call when I need gas. They are happy to bring a 100 gallons or more anytime.
Ooops meant to CC AlmaKing.
Propane tanks have valves that release pressure, if there’s too much pressure in the tank. I saw one of these fail spectacularly on a 100 degree day on a 500 gallon full propane tank. The cover blew off, flew about 30 feet. Then the propane all leaked out over the next 2 days.