(almost) 1 year old suddenly cries at bedtime?

Ashley๐Ÿฆ‹ โ€ข [Married]๐Ÿ’[Mommy] ๐Ÿ‘จโ€๐Ÿ‘ฉโ€๐Ÿ‘งโ€๐Ÿ‘ง #girlmom [๐Ÿ‡บ๐Ÿ‡ฒโค๐Ÿ‡ณ๐Ÿ‡ฎ]

My daughter has been a great sleeper since 4 months. I would lay her down and she would fall asleep within minutes. But as she got older it would take her about 15 to 20 minutes because she wanted to play, lol. But anyway, about 2 weeks ago, she started hysterically crying when I left the room after I would lay her down, so I ended up rocking her to sleep for 5 straight nights, and then all of sudden things went back to normal. Fast forward to 2 nights ago, it started again.๐Ÿ˜ฆ And it's just during nighttime, she does fine for her naps. Any idea what this could be? Thanks in advance!!