"Pending" custom link in menu issue

Every time I try to add a custom link to a menu, it shows up as “Pending” and will disappear if I try to save the menu. I’ve googled this issue and the solutions are to switch to another theme and back, or to repair the wp_postmeta database. I’ve done both and have had no success. This issue only occurs with custom links – posts, pages, categories work fine. This is driving me mad!