[T-Mobile Galaxy Note 4 Q&A, Help & Troubleshooting] febzz88:
I started experiencing this issue since last week. Out of nowhere, my Note 4 started to lag and freeze. At first I thought maybe it was the battery too, so I got myself a brand new Anker Battery. And hey, nope it's not a battery issue. Then I reformatted my phone, and yes, it was still lagging and freezing.

Fast forward to this week, last night, I got the mmc_read failed message. Shoot me.

Now I've been using the Wake Lock app and it's set to Level 4 (Partial Wake Lock). It's been much better with this App running. Of course, my battery takes a hit. But at least the phone is usable, as long as I don't restart the Phone.

My gf's phone is exactly the same as mine, Note 4, and we're exactly on the same firmware version. She has no issue at all. We've switched batteries as well and her phone works fine with any battery.

I never rooted my phone, and I've been using only the original, official firmware pushed by T-mobile. My phone is running the latest firmware (EQB1) released last month. The problem didn't start right after my phone was updated. Only since last week.

Now, I've been scouring the Internet and many say this is a hardware issue, but some say too that this is probably caused by the firmware. Does anyone now know better if this is a hardware or software issue?

I was going to get myself another Note 4 but then if this is a firmware issue, it could happen too to a new Note 4. If this is a hardware issue, then a new Note 4 may not get this problem.

There's also a conspiracy theory saying that Samsung purposely did this so as to force all Note 4 users to upgrade their phones. If this is a firmware issue, can we file a class suit? Sigh.

UPDATE 1:

I just came back from the Samsung Experience Center. I also talked with Samsung, T-mobile over the Phone today.

So basically, from what the guy over at the Samsung Experience Center told me, a few months ago, many Note 4 Sprint users had this exact same issue. Basically the firmware update caused the phone to malfunction. In the end Samsung replaced all the affected phones. I went there, talked to him, and initially I wanted him to reflash my phone but he then told me that this issue was basically a faulty firmware. Reflashing wouldn't really help because the firmware itself is faulty. The firmware could have affected (damaged) the hardware. That this exact same issue has happened in the past with Sprint users.

I then called Samsung hotline up and talked with, fortunately, a friendly and helpful rep who was willing to document everything and escalate the issue on my behalf. She told me that she would call me back in a few days to update me on how the case is going.

At this point, I'll just have to wait and see.

UPDATE 2:

And apparently I just learned that Note 4 in Europe and Sprint here in the US just received a latest firmware update around 300-400mb in size.

"The firmware update description reveals that it brings better stability and performance as well as optimizations for improving battery efficiency. This Galaxy Note 4 update also comes with the March security patch that has 73 fixes for Android OS vulnerabilities and fixes for a dozen vulnerabilities that Samsung found in its own software."

Fingers-crossed, hopefully this update will soon come to T-mobile and other carriers and fix our issue.