Paragraphs: referenced entity error on save I recently updated to Drupal 8.6.2 and Paragraphs 8.x-1.3.

I have a content type with a Paragraphs field. When I try to update an existing node I get the following error message:

The referenced entity (user: 21) does not exist.


The existing paragraphs do not reference users directly.
User 21 does not exist.
User 21 is not the node author.
I can only update the node if delete all of the paragraphs, of every type.
There are no pending db updates or entity updates.


My feeling is that something didn't update correctly, but I'm not sure how to check / rerun the updates. (There were a number of updates to be run when I deployed the 8.6.2 update.)

UPDATE: I rolled back to the previous release and DB state, and I still get the error (which no one noticed), so it is not related to the update.

UPDATE 2: Ticket on drupal.org
User 21 was deleted, but 21 was still stored as the value in the uid column of the paragraphs tables. Changing the uid to that of an existing user (23) solved the problem:

UPDATE paragraphs_item_field_data SET uid = 23 WHERE uid = 21;
UPDATE paragraphs_item_revision SET revision_uid = 23 WHERE revision_uid = 21;
UPDATE paragraphs_item_revision_field_data SET uid = 23 WHERE uid = 21;


Run SQL, empty cache, reload edit page.

Note: other tables also contain the uid 21, but without a (noticeable) adverse effect.

UPDATE file_managed SET uid = 23 where uid = 21;
UPDATE node_field_data SET uid = 23 where uid = 21;
UPDATE node_field_revision SET uid = 23 where uid = 21;
UPDATE node_revision SET revision_uid = 23 where revision_uid = 21;


And two from contrib:

UPDATE crop_revision SET revision_uid = 23 where revision_uid = 21;
UPDATE redirect SET uid = 23 where uid = 21;