We have released a new version of the EN15804 add-on for ecoinvent 3.8, available in Nexus: https://nexus.openlca.org/database/EN15804%20add-on.
The new version has different ref ids than the system process version and therefore both the LCI and unit version of the database can now be combined. The LCIA methods have also been corrected by removing duplicate flows and adding direction to categories.
The database only works in openLCA 2.0.