The problem i'm having is basically the same mentioned there. I had both an OpenVPN and a Strongswan L2TP/IPSEC VPN working perfectly on a stock, non-rooted Verizon Galaxy S4. I get "upgraded" to 4.4.2, and now I can't have either VPN connected while i'm using LTE/mobile data; after about a minute or so of having the VPN connected, the LTE interfaces resets (logo in the title bar goes dim for a few seconds, VPN disconnects.) This effectively renders doing any kind of work over the VPN unusable. The problem doesn't happen over WiFi; only over LTE.
Just for kicks, a T-Mobile forum post suggested changing the "APN" protocol from "IPv4/IPv6" (its default) to "IPv4" to fix a similar-sounding issue. I know I have a Verizon phone, but i figured i would just try it, but it did not help.
Any ideas at all? And, while i can practically predict the answer to this, is there any way for me to revert back to the previous software version without rooting? I will say that a roomate of mine has my exact phone/software version, and i set him up with a VPN connection just to test if the issue happens there; it does.