Hi, erossini, please try installing the Classic Widgets plugin and see if this resolves the issue: https://ww.wp.xz.cn/plugins/classic-widgets/
You could also try using the “Health Check” plugin to diagnose the issue: https://ww.wp.xz.cn/plugins/health-check/.
In the troubleshooting tab, you can disable all plugins and have the theme changed while logged in; visitors will see the website as if the plugin(s) and/or theme wasn’t changed.
In this case, please try deactivating plugins/your current theme to determine if plugins and/or theme(s) are causing your issue.
If it turns out to be your theme or a plugin, it would be best for you to contact the theme/plugin developers to sort this out.