I don't know what you mean with the jevuser custom field?
I think I may need my eyes tested again - I missread "administrator/components/com_jevents/fields/jevuser.php" as the custom fields plugin file "jevruser.php"
There is something strange about your asset rules tables since this line refers to core.admin permissions (which is the right to managed com_categories) and implies it is not set or is empty.
There is a workaround - change line 101 of "administrator/components/com_jevents/fields/jevuser.php" to read
$creatorgroupsdata = isset($creatorgroups["core.admin"]) ? $creatorgroups["core.admin"]->getData() : array();
I'll include the change in the next release.