Hello!
Last night my hoster changed the php version of my account from PHP 5.5.38 to 7.2.1.
Now I found more than 90 pages with the same error in the error protocol. 
Here' an example. The lines written in red are the same everywhere, the others are mostly different:
W4FfEyTf6lpT7fBqxHFmilZrES6gH10w
Type of error: General
Unknown Error: The each() function is deprecated. This message will be suppressed on further calls
https://forum.xxx.de/index.php?action=mentions;sa=fetch;api=json;lastsent=0
File: /www/htdocs/w00f7xxx/forum/sources/subs/UltimateMenu.subs.php
Line: 41
Line 41 in the UltimateMenu.subs.php is the 3rd here -> while (list(, $row) = each($db_buttons)) {
// Insert the items in to the site menu as defined in the um ACP
reset($db_buttons);
while (list(, $row) = each($db_buttons)) {
// UM menu button basics
$temp_menu = array(
'title' => $row['name'],
'href' => ($row['type'] === 'forum' ? $scripturl . '?' : '') . $row['link'],
'target' => $row['target'],
'show' => (allowedTo('admin_forum') || count(array_intersect($user_info['groups'], explode(',', $row['permissions']))) >= 1) && $row['status'] === 'active',
);
What's wrong there?
.