Villagers level from Apprentice (level 2) to Journeyman (3) with 70 XP. However, the experience bar shows that they need 110 XP to level up. This leads to the villagers leveling up much earlier than expected.

They also level from 3 to 4 with 150 XP (despite appearing to need 170). The other transitions, from 1 to 2 and from 4 to 5, display correctly.

This was a bug in 1.14.3 as well as 1.14.4-pre6, but the exact numbers appear to have changed. The numbers above reflect 1.14.4-pre6.

I attached a video demonstrating this on an Armorer, but it appears to be a bug on all villager types.