This happens mostly when you change the path (directory) of your string table, i got a fix for you, a very easy one.
right click on your string table and open reference viewer, it will display all blueprint classes or widgets associated with the string table.
open each one alone and inside each blueprint class or widget press Ctrl+F and search for “MISSING STRING TABLE” and assign each one of them with their original string table key.
if you foret the OG string table key just hover on them while they hold the value “MISSING STRING TABLE” and it will show the old key with the old data string table path.