No pseudo-site found in root line. of page N
Sometimes (very often but somehow not every time), when creating a new sys_category record AFTER an existing one, this error pops up:
It is worth mentioning that the "7" is not a page UID but the sys_category UID instead.
From Web > List, click to add a record after an existing one:
The other way to reproduce is while editing a sys_category record and adding a new one:
Note: Maybe this helps but I'm on the site root page...