LISP loading, not finishing, no errors.

[BlackBox]

... so lesson for me here, is to never assume that certain layers will be present

You could always create the layer, or at minimum notify the user, if the desired layer does not exist:

(if (tblsearch "layer" layerName)
  ;; do work
  (prompt (strcat "\n** \"" layerName "\" layer does not exist ** "))
)

... At least that way (notifying the user), they know what's wrong, either to fix themselves (by creating/renaming the layer), or can include that useful information when reporting the issue to you.