On version 2.1.12 when I click on backups in the admin menu I get the below
There has been an error processing your request Object DOMDocument should be created.
In the logs I see this.
[2018-03-24 12:28:33] main.CRITICAL: Warning: Declaration of Magento\Backup\Model\Backup\Interceptor::getFile() should be compatible with & Magento\Backup\Model\Backup::getFile() in /home/staging/public_html/var/generation/Magento/Backup/Model/Backup/Interceptor.php on line 7  
I have googled but cant find anything with this issue, has anyone ever seen this before? Seems to be the only admin menu doing this. have deleted var/cache, page_cache, generation and view_processed and deployed static files but no fix.