Cannot Update Menu

Part of my menu went missing and I cannot update it. Running theme Thesis 1.8.5 but no change when switching to 2013 theme. No change when plugins are deactivated. Recently updated to WP 3.9.2 and Thesis 1.8.5 at the same time, but problem might have been pre-existing – hard to tell because of other problems related to previous version of Thesis theme. I can add items to menu and Save, but the revised menu does not save and the Manage Locations Primary Menu reverts to “- Select a Menu -“. Re-selecting the correct menu makes no difference. Any ideas? Website is classiclightweights.net