M96 Hard Lockup

I'm hoping that someone can help me with a very annoying issue.

At some point recently, my M96 began to hard lockup while using the device. By "hard lockup", I mean I cannot interact with the UI, I cannot connect using adb, I can't access the device at all. The only thing that solves the problem is a hard reset (holding down the power button for 5-10 seconds). This problem occurs fairly regularly, sometimes only a few minutes after powerup, which, as you can image, is rather frustrating (especially since I love the device otherwise!).

I've tried to use catlog to capture the logcat entries just before the lockup, but I haven't been able to discover anything useful.

I have the Arta-Tech version of the M96, all updates have been applied. I'm rooted, but I can't remember if this started happening before or after I rooted the device. I have a lot of ebooks and PDFs on my external SD card (i.e., PDFs in the thousands), so I don't know if that is causing any problems. I also have my Wifi set to auto disable after a period of time.

Any suggestions of what could be going on? Or others who have had this problem? I'm trying to figure it out without doing a full factory reset...