sync's stop after a few days on LG G3

very odd problem, I have 4 users with LG G3 phones, 1x verizon, 2x tmobile and 1x AT&T, all experiencing the same issue.

Everything works fine for 1, 2 or maybe even 3 days, then the devices stops updating. If you hit refresh it says it refreshed, but it did not. I've resetup each account numerous times on the devices and taken to forcing all EAS versions to 2.5, but to no avail. If I reset the device it starts working again, but again for anywhere from 24 to 72 hours or so...

Any ideas on what to try would be appreciated.

Running server on
Ubuntu LTS 14.04
Zimbra 8.6.0_GA_1153.FOSS
Zextras 1.10.2
1 server
Linode VPS with 8 cores, 16GB RAM and 384GB storage (35% used storage)