Strange Nighttime Occurrence in Old Village

When I returned to my home base and visited the nearby village of 34 villagers, nothing was normal. Although it was night, almost every bed was empty but villagers stood around in the larger houses like it was before beds were introduced. I broke the empty beds, reset new ones and villagers returned to beds, all but three. So three established villagers were gone and 15 new villagers unnamed and without jobs were spawned. The five golems still occupied the fenced and well lit village as they have for five years. What happened to this village? If only three were missing, then why wouldn’t the established villagers or the newcomers occupy the all those empty beds? And most of all, could this happen again?