Hi @sinyb 

According to the documentation, fast Mode synchronization, which increases the upload frequency from the mobile device to the server. Fast Mode synchronization shortens the sync interval to five seconds when messages are ready to upload. In your device, if the messages are ready to upload, it will changes the sync interval to 5 seconds. When uploads are complete, the sync interval returns to the value you specified in the admin > sync interval. hope this may help.

Hi,

Thanks for your answer. Yes, I am familliar with the documentation. 

However, my issue is that the fast mode synchronization is not working, and I was wondering if there is any place to enable/disable this functionality, or should it work with the OOTB functionality?

According to the Release notes: Fast Mode is disabled when there is no connectivity or sync errors to resolve.

Fast Mode shortens the sync interval to five seconds when messages are ready to upload, but have not been uploaded in the last regular sync cycle.  Fast Mode does not get enabled as soon as an update is saved on the mobile device.  The normal sync cycle runs at the set interval.  During the next sync cycle, the sync engine will try to upload a batch of messages.  If all queued messages get sent to the mobile service in the sync cycle, the sync interval remains the same.  However, if there are still messages queued that have NOT been sent to the server, then Fast Mode is enabled.  Once all messages have been sent, Fast Mode is disabled.  

This feature is designed to speed the uploading of large numbers of messages, especially if the user has been working offline for awhile and returns to an area of connectivity.  The best way to test the feature is to put the device in airplane mode (or pause sync) and make dozens of updates so that there are dozens of messages in the queue.  Then go to the sync screen and watch how fast mode is enabled after the first sync interval after returning connectivity to the device.