Depending on the version you updated from, JavaScript code might have changed with the update.
Perform a force refresh in your browser (pressing Ctrl+F5 or Ctrl+R several times) to make it load the latest copy on all files and check if the issue persists.
If it does, it may be caused by a plugin which is no longer compatible with latest WordPress version (if you updated that too). Try to cycle your active plugins on/off and check if/when the issue goes away in the theme.