Hi thanks for repoting the problem.
AnkiTerminator cannot update while the sidebar is open, normally the sidebar auto closes when updating so this problem does not occur, but in your case it seems to be failing for some reason (another add-on maybe interfering?).
There is an action in the menu to manually close the sidebar, so use that to close the add-on, then try updating again. (Tools → AnkiTerminator → Completely close Sidebar)
If that doesn’t work, try disabling the add-on and updating. (AnkiMenu → Tools → Addons → Select AnkiTerminator → Toggle Enable → Restart Anki → Update addon → Toggle Enable → Restart Anki)
If these steps do not resolve the problem please contact me again.