Bit of a weird one. In 13.1.2 my Memoji changes are not reflected on my iPad Pro. They sync via iCloud Drive. You can see this by disabling iCloud Drive in settings: your Memoji vanish from your iPhone and return upon enabling.
Sync was working in earlier versions of iOS 13.
I asked a friend to check it out on his devices — his phone and iPad mini sync, his iPad Pro does not.
Can any of you folks see changes or additions to Memoji reflected on all your devices?