I got the same issue on my Nexus 5 as well. I'm currently in China, Google, Facebook and Twitter are blocked. But it worked fine few weeks ago, I mean "No exclamation mark", and since I had lived here for like 3 years and now this annoying thing comes up. It got 2 exclamation marks on both Wi-Fi and data roaming right now, and one more ridiculous error is whenever I turn on my Wi-Fi, not connected to any Wi-Fi yet, it still shows up with that mark, after connection, still there. My Nexus 5 is not rooted. What really funny is my connections are fine, both Wi-Fi and data roaming, it loads really fast, I can download things with at least 1MB/s either the connection is. And yet, I admit that sometimes when I walk on the street, my data roaming shows up with LTE or H and no exclamation mark, after I walk away from that area, it shows up again. With Wi-Fi? I tried KFC's, restaurants, anywhere I could but still there.
Still, I hate that exclamation mark, searched and tried:
1. APN - Failed
2. Forgetting/Re-adding Wi-Fi - Failed
3. Turn on both Wi-Fi and Data Roaming - Failed
4. star#star#4636#star#star - Failed
5. Wipe cache partition - Failed
6. Update from 5.0 to 5.1 - Failed
7. Using New User - Failed
8. Reboot - Failed
9. Sim card out-in and different card - Failed
Anyone got any idea? I'm dying of looking at those marks helplessly!
Help!