hello, check are there any errors on browser console (F12). Also in which browser do you test it? Did you try to do the same in other different browser.
Are there other term store administrators? Is problem reproduced for them?
If all of these won't help you - try to check ULS log (you may copy url of term store page and find correlation id for request for this page. Then filter records by this correlation id and see all related records. There is convenient tool which allows to filter ULS logs: ULS log viewer)