Align center is not available on select visible buttons in formatting toolbar. Only align-top and align-bottom appear in my version. Align center is available in menu | format | align center.
Created attachment 146369 [details] screenshot lo 6.1.3.2 win 10 I can't reproduce it. To be certain the reported issue is not related to corruption in the user profile, could you please reset your Libreoffice profile (https://wiki.documentfoundation.org/UserProfile ) and re-test? I have set the bug's status to 'NEEDINFO'. Please change it back to 'UNCONFIRMED' if the issue is still present
Resetting the user profile solved the problem.
Closing as RESOLVED WORKSFORME