My 5mo wakes up btw. 2-4am

My 5mo recently started waking in the middle of the night. She doesn’t cry or anything but after awhile she will start to sing which ultimately wakes my husband and I up which at that point it’s showing that she’s been awake for 30-40min already.

She goes to bed between 6:30-8pm every night and I make sure our routine is consistent or close to on schedule. She was sleeping through the night for almost 2 months now without needing a bottle or anything and all of a sudden she started this. I’m due to go back to work and just concerned that this is becoming