I have a strip of 30 neopixels, split into two 15-pixel pieces, connected by a 2 foot length of three wires, soldered directly to the strip. I have three copies of this setup. All three worked fine for a couple days, then I damaged one by soldering while it was turned on. I seemed to fix that problem by removing the dead pixels, and jumping the DIN-DOUT connection over the dead ones. After that, it worked fine again for a day, and then I screwed up again by disconnecting power while a micro was still connected. Now, the first 15 pixels work fine, but the last 15 don't.
Troubleshooting:
None of the pixels are burnt out - I can temporarily attach a DIN at any of them and that one, plus some number of further pixels, work fine.
All of the connections near the point of failure are good, as far as I can tell by checking continuity with my multimeter.
I'm out of ideas. Any help?