maybe an other villager has taken his workstation, you could check if that's the case by blocking the path of other villagers to the lectern and replacing the lectern
this bug begins in version 1.14.4, but I couldn't figure out how to put other versions in the versions box
maybe an other villager has taken his workstation, you could check if that's the case by blocking the path of other villagers to the lectern and replacing the lectern