The error clears on a reboot - but that's not really acceptable. Nor is adding another app to fix what is clearly a bug.
Hi all, I just got an LG G5 se and was experiencing the same issue. (Go to settings/account&sync/yahoo it stated "sync not working try again")
No one seemed to have an answer that didn't involve pulling the laptop out. So I thought I'd try changing the settings within the yahoo mail app... Bingo. Default is to not sync contacts, allow sync here and when you attempt to sync in settings and the missing link is restored. All contacts successfully copied without excel or a 3rd party app.
How to:
Open yahoo mail app and sign in
From mail area of app (not news), click menu button {3 horizontal lines}
Open "settings" scroll to "sync contacts"
Ensure slider is filled with colour indicating this function is 'on'
If prompted, allow yahoo to access device
Revert to device settings and attempt sync.
Worked for me, hopefully will work for others