What do you mean by “articles” (is it wiki pages?) and what does “restore from xar” means? Does it mean you didn’t perform an XWiki upgrade as indicated on https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Upgrade and that instead you did a backup/restore of a XAR?
This simply means that the extension you installed and that brought the Admin.RunShellCommand wiki page is using some deprecated velocity call. It’s not a problem but that extension should be fixed or you should upgrade it if there’s a newer version.
I have strong suspicious that it was done in this way. Backup XAR and restore it on fresh 15.1.
I tried update from 15.1 to 15.2 and updater show me that I have broken “base flavor”, even when I tried to Install new versions of extensions I still end up with warnings about velocity. How can I fix this extension? I don’t know how to edit it.