The bug

Villagers will breed more than there are free beds in the village, even if all the beds are close to the villagers (i.e. they should have no problem detecting them)
This is most likely to happen in the late afternoon right before the villagers goes to bed.
This has been a problem since version 1.14.4

How to reproduce

1. Make a confined area with lets say 40 beds
2. Spawn in one adult villager pr bed, in this case 40
3. To ensure they are all bonded to a bed, make them sleep in the beds at least once (set time to 12000 ticks and when they are all sleeping set the time back to day again)
4. Give them plenty of food to make sure they can breed
5. Set the time to around 11000 ticks
6. Observe some of the villagers right before bedtime (12000 tick) will produce a baby resulting in there being more villagers than beds.

Example