Activities Sync - Meetings, Task and Calls

We have 4 users that use the activity sync. 1 user works all the time (Samsung note, Caldav version 0.4.27) and the other 3 (Samsung Edge7, Caldav version 0.4.32) continually stop syncing. Unfortunately, our CEO is one of the people it stops syncing on. However, these same users stopped syncing on the old set up which is why they upgraded to the new version of Caldav to see if it would work. It connect fine and performs the sync when you ask it to manually sync, but it does not continue to sync at the set intervals which is causing lots of missed appointments. What do you need to assist us with troubleshooting the issue before they abandon the product? I am the user that it always works on so I don't want it to be removed.