I've finaly found the time to debug my problem with nconf after upgrading my Ubuntu system.
grouping (name of a column) is a mysql keyword since 8.0.1 (see https://dev.mysql.com/doc/refman/8.0/en/keywords.html for keywords).
Fix is to change any query from grouping to `grouping`
I dind't make a pull since I've messed up my nconf quite a bit searching for the error but would like to let you know
Edit:
And it seems disabling a single service for a host now is broken, no services at all are returned from the query so the host has no services associated. Tried this with an old version running an older mysql instance the same query works as it should. If one service is disabled the query results NULL in my mysql 8 envorinment, in 5.7 it shows the remaining services. Switching no to yes results in the expected disabled service returned in 5.7 and in 8 it's still NULL as long as at least one service is enabled
SELECT ItemLinks.fk_id_item AS item_id,'','<HOSTID>' FROM ConfigValues,ItemLinks,ConfigAttrs,ConfigClasses WHERE ItemLinks.fk_id_item=ConfigValues.fk_id_item AND id_attr=ItemLinks.fk_id_attr AND fk_id_class=id_class AND config_class = 'service' AND (SELECT naming_attr FROM ConfigAttrs WHERE id_attr=ConfigValues.fk_id_attr)='yes' AND ItemLinks.fk_item_linked2='<HOSTID>' HAVING ((SELECT attr_value FROM ConfigValues, ConfigAttrs WHERE id_attr=fk_id_attr AND attr_name='service_enabled' AND fk_id_item=item_id) <> 'no' OR (SELECT attr_value FROM ConfigValues, ConfigAttrs WHERE id_attr=fk_id_attr AND attr_name='service_enabled' AND fk_id_item=item_id) IS NULL) ORDER BY attr_value