Sleep Mode Locking Feature Stopped Working

My apple watch isn't locking when in sleep mode after a recent update. (Not sure if "locking" is the correct term.) It enters sleep mode (dims screen, silences notifications, etc) but I can still swipe / tap the screen, crown, and button. Previously, I had to turn the crown to unlock and prevent accidental actions. I use the watch to track sleep, but I'd like to avoid accidentally making a call, sending a text, etc.