Using 'base hook' in the theme hooks doesn't find theme suggestions (e.g. layout--onecol -> layout--onecol--node).
This has been a struggle for Display suite, see #2802429: Display layout twig not overridable..
A work around is to explicitly define 'template_preprocess_layout' in the preprocess functions key.
(needs a better issue summary)
Also, wondering whether this qualifies for 8.x-3.x directly since it's quite the annoying bug.
