[horde] ActiveSync Ping/Sync flooding in webserver log

[Volker Then]

Hi Mike,

I have activesync problems with two clients, both using Outlook  
15.0.4945 (and alos Outlook 16), and both are flooding the webserver  
log with Ping/sync requests.

In the device logs I found lines like this

NOTICE: STATE: Error saving state, checking if this is due to previous  
synckey {596f159b-37c0-4f03-aaa9-2a9494fb36a2}3 not being accepted by  
client.



[31116][2017-07-19T12:29:47+02:00] ERR: Permission Denied
[822][2017-07-19T12:29:47+02:00] INFO:  
----------Horde_Core_ActiveSync_Driver::authenticate() attempt for  
*********_wagner----------
[822][2017-07-19T12:29:47+02:00] INFO: ----------PING request received  
for user *********_wagner
[822][2017-07-19T12:29:47+02:00] INFO: ----------Request being handled  
for device: C7192254727E416BB3F0D430B5363C9E, Supporting protocol  
version: 14.0, Using Horde_ActiveSync v2.38.6


[886][2017-07-19T12:29:43+02:00] ERR: COLLECTIONS: Attempting to add a  
collection
                     to the sync cache while requiring a synckey, but no
                     synckey could be found. Most likely a client error in
                     requesting a collection during PING before it has issued a


Both users share their resources (calendars) with each other and other  
users. Syncing on iOS and Android, both native and Outlook work  
properly.

What can cause the issue? I tried to remove the device and resync. No  
success. Removing and reinstalling the accounts on Outlook, no success.

Regards,

Volker