First null pixel as level shifter fine, all pixels afterwards flicker

[XmasinVancouver]

Using a Wemos d1 mini with the pixel stick firmware. Have a few of these and they all work great. I use a sacrificial pixel as a level shifter and null pixel as described here https://hackaday.com/2017/01/20/chea...-3v-data-line/

I did the same thing last year and it worked great. In fact, an identical setup for 180 pixels is on one column and works without issues. The other column, the first pixel/level shifter/null pixel is stable and working fine, then there is about an 8' cable that connects to the column before the actual pixels. When running a test sequence of any kind, the pixels are flickering like strobes. About 40 pixels in I have a jst connection where I joined two strings. If I disconnect the jst while it's flickering, everything past that point will then stay steady on without flickering, but the initial pixels going back to the stick are still flickering. Re connecting the jst will make everything flicker again. I'm assuming this would probably rule out a simple lack of power issue and point to data corruption or something like that. That first pixel near the controller is fine, it's not until the first pixel that it flickers. Wondering what the likely culprit is? I have a hard launch on Tuesday and I'm running out of time to go down the rabbit hole

[MartinMueller2003]

I have to ask the basic question: Is V- properly connected between the Null Pixel (NP) and the rest of the string? What you are describing would cause me to look at a few things:

V- from NP to rest of string.
Data from NP to rest of string
NP Output section or first pixel Input section has gone bad. Since they are far apart I would replace the NP first.

You did not mention any connectors between the NP and the first pixel. If there is one it may be having an issue.