Hi Leonardo,
Thank you for the information. If it's a CentOS installation, then there is a limit to the suggestions we can offer, as some of the available packages may be different. However, several community users have shared CentOS installation guides, so you could check your installation against these:
Please note that in general, we do not test these instructions ourselves.
I would also recommend that you review this section of our upgrading docs, to see if there are any fixes you need to make to your custom theme:
I also suggest that you try running the CSS recompile commands I recommended in my last post, against both the Dominion base theme, and your custom theme.
Finally, it's good to see that the clipboard page itself is accessible, but it seems that clicking the paperclip icon to pin a record is not working for you. I suggest checking your webserver error logs to see what the related error message is for the 500 error you saw when trying the clear clipboard option.
Of course, if you are able to upgrade to version 2.5.4, it may help as well - I'm not sure if it will help solve this particular issue, but you will find a number of enhancments, new features, and bug fixes.