Despite what others have said, as a moderate seller (a few grand a month), I still have the 8 relists for auctions. Very occasionally the option might disappear. It generally reappears after a cache and cookie cleanout. If not, it's there the next day.

Maybe even try a different browser. I have been a Chrome Junkie since it came out. Lately, Microsoft Edge has been loading stuff that Chrome won't (on a laptop). It's certainly worth looking at. Just make sure you install an ad blocker first!

Edited to add: If you do decide to do a cache cleanout, make sure you set the dropdown to "all time". Untick the password clear out if you want to keep your saved passwords.