Love and Treasure Quest

Are you playing with enhanced lighting? Sometimes it helps if it’s switched off.  If this didn’t help, I’d download my game to a different device. If you don’t have one, a family member might help out with their’s.  When your town is on that device, try to enter the island and complete the quest.  Next would be to upload the game on that device, reinstall the game on the main device and download the save data.  
  If all this didn’t help, reach out to the Online Support within the game:    
Tap the three dots at the bottom right, then info -> Online Support -> the square talk bubble at the upper right. It’s not a real time chat, so it may take a while until you get an answer. 
(I’m not sure, what’s meant with “reached out to EA”, so you might have used that way already.)