I have a problem with the guide groom node while working with hair. (I'm using H19.) I'm working through Rohan Dalvi's Hairy Houdini course, and he adds ramped color to the hair with an attribute wrangle in a for-loop--which is straightforward enough. The problem is that copying that for-loop from one section of hair/one guide groom to the other breaks the guide groom--the hair all disappears. Making a new for-each loop takes no time, but the bigger problem is that once I go back upstream to the guide groom, all hair has disappeared--something not working downstream appears to retroactively break it. What is happening? I've reset the viewport, I've reopened the file, none of that works. If I reset the guide groom it reappears, and I can brush it, and it even appears to work at the end of the for-loop that applies the color, but the minute I go back upstream and highlight it again, all the hair has disappeared. Is the H19 guide groom just super-buggy? I'm on 19.0.455 (I think that's the latest one with V-Ray, hence not the latest version, but far from the earliest.) I'm running Windows 10, although I don't think that matters.

Oh wow. There is also a bug where this happens using a Guide Transfer node. The upstream guides vanish forever, even undoing doesn't bring them back. I filed a bug report with SideFX yesterday, you might want to do the same, assuming no one here posts a solution.

Glad to hear I'm not just doing something moronic. (Probably.) I'll hold off on the hair until we see what 19.5 brings!

The guide transfer bug is still present in 19.5. Since it's so similar to yours I'm assuming they're related. Hopefully a fix is coming!