Villagers Disappearing

Put the summary of the bug you're having here

What I expected to happen was:
Villagers to continue to exist, or to be killed by things determinable.

What actually happened was:
Despite bringing over more villagers from a nearby village, and breeding the villagers, the overall population continued to decrease randomly. We secured the perimeters of the village, and lit the area within, so that no notable amounts of hostile mobs could spawn or enter the village. Nevertheless, the occasional villager disappears, even when we have traded with them to a higher level.

Steps to Reproduce:
There does not seem to be a pattern to reproduce the disappearance. Only that the other villages nearby have not faced such an issue. Furthermore, upon searching online, others seem to encounter similar issues.

When I searched reported bugs, I did not seem to find anything similar to this, perhaps because it is such an illogical issue. There does not seem to be a pattern to why this happens, and it appears to be beyond the simple and frustrating stupidity of the villagers AI.

Therefore, I understand it will not likely be any sort of easy fix, but I wanted it to be stated and recognized, so that we can at least have the comfort that something will be done to end this specific frustration someday.

It has costed us a lot of resources fighting this illogical issue within the game. It would be nice to have the fight brought to where it can make a difference.