Is it summer where you live? The days are longer? More time to be active for a kitty! My bengal sleeps through the night until the alarm goes off in the winter time. But, in the summer time he wakes me up around 3 to 4 a.m. Why? I don't know! He has dry food out all night. Some nights I get up and feed him wet. Other times, I tell him to lay back down and go to sleep. If I let him cry for a while, he will eventually come back to bed. This is really common cat behavior. The fact that you let him outside should make things easier as he doesn't feel cooped up.
The ONLY thing you can do is ignore the cries. Jackson Galaxy says it takes two weeks for the behavior to change -- and those two weeks can be exhausting. But you just have to be patient and diligent. Now, if he is sensing another cat roaming around your home during the night, that could set him off. Mine will start howling if he sees another cat walking by a window. Even though you may not see or smell another outdoor kitty -- your cat's sense of smell is 14 times stronger than ours. You say nothing has changed -- but something has! You just have to figure out what it is, deal with it, and things should go back to normal -- somewhat. Things are never normal if you have a bengal.