If you think that Yahoo mail has stopped syncing then, the very main thing you have to do is to-
- Check the Yahoo mail current version and update it if it gets old
- Also, make sure to turn on the synchronization in Yahoo mail
- There might be server settings that get corrupted and hence, you are facing syncing issue
- If you have checked all of this and still the error persists then, update the operating system
These are the instant fixes for Yahoo not synchronizing and if you think that the error persists again then, getting in touch with yahoo customer care Phone UK will be great to get it fixed.