The new villager AI makes every villager want to work. The Farmer, which used to be the only villager who actually did something different prior to this update, no longer harvests crops. They're too busy looking at the composters instead.
Linked issues
duplicates 1
Comments 2
A cause for this issue was found later; see MCPE-47166.
This appears to be fixed in the latest version - Farmers were harvesting and replanting crops.