Currently the MOD endpoint does not support such large queries
Virtuoso 42000 Error The estimated execution time 869218 (sec) exceeds the limit of 40000 (sec)
So either refactor the query or set hte limit on the MOD endpoint up.
Refactoring the query would be far more simple (e.g. just split it to avoid the UNION)
Until then discovery via void mod will be switched off.