The error message given when a person tries to save an entity form while it is referencing a disallowed user can be misleading, saying for example that "The referenced entity (user: 4) does not exist." when in fact user 4 does exist, but does not have one of the roles permitted in the entityreference field configuration.
In most configurations the widget will be an autocomplete, or even a select, so invalid users will never be shown. However this can come up for people who copy paste because they know what input is expected and already have it, probably in entity pre-populate types of scenarios, and most commonly i bet when a user has been referenced with the autocomplete widget, the relevant role is taken away from that user, and somebody coming back to the form tries to save it (without even changing that user reference field).
The problem is that they will panic that the user got deleted somehow, then find it and see that it is there, and still not understand that in order to successfully reference that user they need to add the role back.
Ideally, give a clear, specific message such as "The referenced entity (user: 4) must have one of the allowed roles (Editor)."
If not, vague but accurate messages such as "The referenced entity (user: 4) is not valid for referencing here"
Better messages.
None?
None.
None.
Thanks for the report.
If this problem was discovered on a version of Drupal that is not 11.x, add that information in the issue summary and leave the version at 11.x. In Drupal core changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to the Core change policies → . Also mentioned on the version → section of the list of issue fields documentation. Thanks.