Comment 2 for bug 1741814

It looks like it is a php 7.1 issue.

The line that is throwing the error is trying to do an arithmetic operation on a string that it's not a number:

$offset = (int)($offset / $groupsperpage) * $groupsperpage;

where $offset='all'

And according to the php documentation, with 7.1 we will receive these warnings when performing an arithmetic operation trying to coerse invalid strings:

http://php.net/manual/en/migration71.other-changes.php