Thanks for reviewing.
I don't think [error] Session has not been set is related to the update hook though as the documentation for hook_post_update_NAME states that a return value can be string|null:
string|null Optionally, hook_post_update_NAME() hooks may return a translated string that will be displayed to the user after the update has completed. If no message is returned, no message will be presented to the user.
This issue appears to cover the same/similar session error: https://www.drupal.org/project/entity_print/issues/3383187 🐛 Unexpected error with print engine PhpWkhtmlToPdf or DomPdf: Session has not been set Needs review
I'm not sure if this was caused by something specific to our multisite setup, #17 didn't work for us.
In our case, base_path() is coming through as '/uk/', and $path is an absolute URL including the host and scheme (https://site.example)
As such, $path does not start with /uk/, so the regex doesn't replace anything.
Uploading a new patch to handle as absolute URLs.
Updated #11 to fix "Entity queries must explicitly set whether the query should be access checked or not" errors in Drupal 10
Thanks jrockowitz, webform-repair fixed the underlying issue with missing/broken config so this patch isn't needed anymore.
Just realised there are a number of instances of preg_split with the same issue, so I've uploaded a new patch
JamieP → created an issue. See original summary → .