Steps to reproduce the issue

Create two menu entries listing categorise with subcategories.
One is layout print one layout default.
index.php?option=com_content&view=categories&id=9
index.php?option=com_content&view=categories&layout=print&id=9

Actual result

The router picks always the print layout item because
this entry was added last to the menu table.

This problem will afflict every component if
entries with same attributes but different layouts
exist.

System information (as much as possible)

Issue exist since 3.5 or whenever the router was changed.

Solution / Fix

The issue is caused by a unnecessary simplification in
the buildLookup function of MenuRules.php

$this->lookup[$language][$view . $layout][$item->query[$views[$view]->key]] = $item->id;
$this->lookup[$language][$view][$item->query[$views[$view]->key]] = $item->id;

and

$this->lookup[$language][$view . $layout] = $item->id;
$this->lookup[$language][$view] = $item->id;

I don't understand why both keys are set. It is completely unnecessary.
You can safely remove these two lines because $layout is always set.

$this->lookup[$language][$view][$item->query[$views[$view]->key]] = $item->id;

and

$this->lookup[$language][$view] = $item->id;