Unlike other input fields that have "maxlength" attribute, multiselect doesn't have one. So creating a new host or template with a new group, the entered name can be really long. Currently API hostgroup will return error "Invalid parameter "/1/name": value is too long.", but as for inline validation ZBXNEXT-7410, the error is not visible to user. The error message is in console "Validation error for missing field "/groups_new/0": This value is too long."