I have the same issue and i think it's perfectly reproducibly it:
- Lock it on 2G by using 3G/2G/Dual applet. yappari still works fine.
- Then make a phone call. The 2G data connection symbol gets a red line.
- After the call ended, the red line goes away, internet browsing is still/again working fine. Yappari says still connected but whatever you send ends up with grey mark. Only help is restarting Yappari. 100% sure way to fix it.

That does it for me to reproduce it. Keeping it on 3G, in a good environment of course doesn't have the problem with calls because 3G can handle data and voicecalls at the same time. But 2G can't. And that's where I see my problem.

Why the lock? I do lock it at 2G sometimes to save battery, as yappari is v happy on 2G, data trhoughput wise. Apart from the dreadful not-seeing-it's-disconnected problem after losing the data connection due to a call (or possible other data drops).