Issue happens when using an http_login customized alternate login 
page. Moving Horde_Registry::appInit at the beginning of the 
customized login page solved it.

Since 7.2 , got these errors :

HORDE PHP ERROR: ini_set(): A session is active. You cannot change the 
session module's ini settings at this time [pid 14215 on line 159 of 
"/usr/share/horde/pear/php/Horde/Session.php"]
HORDE PHP ERROR: session_set_cookie_params(): Cannot change session 
cookie parameters when session is active [pid 14215 on line 175 of 
"/usr/share/horde/pear/php/Horde/Session.php"]
HORDE PHP ERROR: session_cache_limiter(): Cannot change cache limiter 
when session is active [pid 14215 on line 177 of 
"/usr/share/horde/pear/php/Horde/Session.php"]
HORDE PHP ERROR: session_name(): Cannot change session name when 
session is active [pid 14215 on line 178 of 
"/usr/share/horde/pear/php/Horde/Session.php"]

Unfortunately count() is used in too many places expecting an array 
when it is not always the case.

A more global solution should be considered other than wrapping every 
count in an if(is_array())

Too many hidden things seems fail. And waiting errors show up in the 
log doesn't seem a good way to fix this.

I'll revert to an older version of php.

Hi,

there are 2 minor incompatibilities with php 7.2

1)
HORDE: PHP ERROR: ini_set(): Cannot set 'user' save handler by 
ini_set() or session_module_name() [pid 2887 on line 95 of 
"/usr/share/php/Horde/SessionHandler.php"]

line 95 can simpli be deleted

2)
HORDE: PHP ERROR: count(): Parameter must be an array or an object 
that implements Countable [pid 7442 on line 371 of 
"/usr/share/php/Horde/ActiveSync/State/Sql.php"]

         if(is_array($this->_changes)) {
           $c = count($this->_changes);
         } else {
           $c = 0;
         }
$this->_logger->meta(
             sprintf('STATE: Saving state: %s',
                 serialize(array(
                     $params['sync_key'],
                     $params['sync_data'],
                     $params['sync_devid'],
                     $params['sync_mod'],
                     $params['sync_folderid'],
                     $params['sync_user'],
                     $c,
                     time()))
                 )
             );

I hope I can publish a cleaner patch here

https://github.com/Ivan-SB/Db