I have a reference LOP referencing in 4 different usds. When I save this out further down the network with a USD ROP set to Flatten Implicit Layers, I get a warning saying that it had to save the reference LOP's implicit layer to the emergency path Houdini generates. I've never had this before with a reference LOP. Normally the layer just gets collapsed, no path required. Any ideas what might cause this issue?

To add to this. There is a sublayer underneath the Reference LOP which modifies the incoming references and it is this that seems to cause the need for a save path. I am not sure why that is though?

I figured it out. I needed to turn of Edit Root layer so that the sublayers became part of the reference LOP layer stack. Again not sure of exactly why this works but it solved my issue.