Thanks for the replies.
New observations:
1) After a fresh TEK flash, on boot, the phone always hangs at the T-Mo splash. If I wait a minute or so, battery pull, boot, I will then get the green "Android Starting/optimizing apps" screen and it boots and restarts fine thereafter. I can consistently reproduce this behavior.
2) I'm using Odin 3.11.1 from Sammobile. The fact that the factory launches reliably, I'll presume that Odin is okay.
3) I was using TWRP 3.0.0.0, I'll try 3.0.2.0 and report back if it makes a difference. For other readers, TWRP tars and zips for 915 here:
http://forum.xda-developers.com/note-edge/development/twrp-915fy-915tmo-moment-t3129459/page10
4) The latest SuperSU and Freeza are good suggestions. I'll report back if they make a difference.
For information:
A) I realized that a /data wipe wipes out SuperSU (which makes sense, with SuperSU not installing in /system anymore), so I'll keep the latest SuperSU on the SD if/when I need it.
B) I discovered that the main branch Xposed causes the phone to hang at the T-Mo splash screen (what I reported above does not have Xposed installed). I have been using N6P since release, so I've been away from Samsung for awhile. I read that i will have to use a custom build Xposed. I'll look into that once I can do more testing with the boot issue. Once it is resolved I will move onto the 910T and 915P. These phones are not my daily drivers, so I can take my time and test.
Cheers.
---------- Post added at 06:52 AM ---------- Previous post was at 06:19 AM ----------
Report:
Newer/latest TWRP made no difference.
Latest SuperSU 2.74-2 made no difference.
Freeza made no difference.
Each separately applied and tested.
The workaround at this point is to do a battery pull after a few minutes and restart.