General :: Data Keeps Cutting Out For 15 Minutes At A Time?

The oddest thing keeps happening to me. Every now and then, my data just shuts off. It is gone for about ~15 minutes to an hour, then comes back on.

I recently bought a used Galaxy S4, and when I first bought it this happened about every day, then it stopped for awhile, now it just happened again (about 4-5 days since it last happened) so I figured I would try to find out what's going on.

But what's happening isn't making any sense. I have full bars, I have t-mobile on the top, I can make calls, and my data is turned on. It's just not working. Turining data off and on doesn't work, neither does resetting the phone. The only thing that works is waiting. When my data is on, I almost always have fast 4g data, I don't have any issues with connectivity.

I took a screenshot of my Settings screen (with private data removed) for reference. at first the only time this would happen is when I would leave a Wi-Fi connection. I figured the phone just was taking too long to "realize" i wasn't on wi-fi anymore and mobile data needed to turn back on. However, I turned off wi-fi for the last week or so and have been using mobile data exclusively. That's when it started happening less, it's happened about every 3 days since I turned off my wi-fi and about every 1 day before then.