My previous trailer was a Keystone Springdale and the automatic switch over never worked. The propane ran equal out of both tanks. So when the tanks were empty, we were REALLY empty. After that first time, I kept one bottle turned off at the valve and never bothered using the switch again. I did this for 8 years. Oh ya, many time I'd have to get up in the middle of the night and turn on the second tank and turn off the first one, but that was much better than running out.
Perhaps your automatic switch over is simply not working. If not, you have the option to switch them manually, or replace with a new switch over.
FYI, my current trailer has the automatic switch over too. I think it does actually work, and works quite well. BUT I prefer to keep one bottle closed all the time. This way I KNOW when I need to refill one tank and do the very first chance I get. I don't mind getting out of bed when it's 5 degrees outside to switch over a tank. But I'd hate to go all night and most of a day (especially if it's a Sunday and everything is closed) with no propane at all because I didn't realize the first tank had already emptied, and now the second one is too!