Allow button text issueBrowser Info Environment
(Tested with current versions of Firefox, Chrome and Safari on Mac)
In any case, I tried to replicate the issue, but it seems to me that your (themes) CSS is conflicting, as it's not the case in Elemental. See attachment.
Please note that the issue can only be seen on Opt-in if the text of the deny button is short and the text of the allow button is long. If the text labels of both buttons are long, the effect cannot be seen. Your image shows text of both buttons of equal length, so it's displayed correctly. If you rename the buttons as in the example attached, you should be able to reproduce the issue.
Tested now on a clean 8.4.0 test installation with Elemental theme.
(Might have to do with min-width: 140px and white-space: nowrap in cookieconsent.min.css)