Sorry to hear about this problem, if I understand correctly you are not able to add a new label to an issue in Jira by just typing in the label value and pressing enter.
I have not been able to reproduce this problem so far, but that screenshot you posted leads me to believe that perhaps there has been an error in the way this particular webpage has been loaded into your browser. I'd be interested to see if this is still happening, if you can open the developer tools or webconsole in your browser to see if any elements on the page did not load as expected.
It might help to try to sign into a new browser or use an incognito browser session just to test and see if this problem exists in other browser sessions. If it does not, that at least tells us more about the scope of the problem itself.
Curious to learn more about this problem.
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