Funny how issues crop up - all at once? Our fav Samsung S2 8.4 tab has started exhibiting exactly the same behavior in that it won't get a GPS lock on the ground unless it's connected to the 'net. Which has become a real problem lately as the tab has started to freeze or lock up occasionally. Often enough though that we've started using two tabs in the cockpit just in case the primary Samsung locks up during a critical moment.
There have been a couple of occasions when the tab locked up and was rebooted in flight that there simply wasn't any 'net available, so we had to resort to the old mark one eyeball on the chart to keep us on track. Hence the second tab.
Can't wait for the new Samsung tab S3 to come out....tried a Huawei Mediapad M3, but the GPS in our particular unit sucked worse than the Samsung so it went back to Amazon. YMMV