Sometimes signing out of your account and signing back in helps with Watch List issues. Restarting the eBay app may help. If you have more than one account, make sure you are signed in to the correct one.
Otherwise, try checking your Watch List using a browser. If you use a desktop browser, you can check if your watch list items appear on your Summary page or on your "All Buying" page:
https://my.ebay.com/ws/eBayISAPI.dll?MyEbayBeta¤tpage=MyeBayNextAllBuying
That may help if the issue is the display of the Watch List page itself rather than any problem with the items on the list.
Some desktop browser users have been having issues lately with some pages not loading properly -- try temporarily disabling your ad blocker, if you use one and are having problems with pages coming up blank.
