If you go into Settings > Accounts > Your email and accounts > Yahoo > "Change mailbox sync settings", there should be a setting at the top to "Always download full message and Internet images". Try checking this and see if it helps.
thanks for replying, have tried this and hasnt solved it, i have seen others with the issue saying a hard reset will be needed. if i do this to reinstall can i just go to my microsoft account and reinstall everything.