It appears that when calculating the amount of players who need to sleep in order to skip the night, that amount is rounded down, which is somewhat counterintuitive (but may well be intentional).

To reproduce

1. Have two players in the same world
2. Run /gamerule playersSleepingPercentage 100
3. Enter a bed
   → 1/2 players sleeping
4. Run /gamerule playersSleepingPercentage 99
5. Enter a bed
   → 1/1 players sleeping