I had the same issue running Foreman3.10, where I wasn’t getting any reports from only a few nodes. I fixed the issue by clicking on the “Edit” button for the affected host, then managing and un-managing the host using the “Manage host”, followed by the “Unmanange host” buttons. This somehow made foreman see the managed server as a host, and the reports came through right away.
My last input above did not do the trick for me. What saved me was the content from this article:
And more precisely, following what was entered above by @Vii-98.
DELETE FROM fact_values WHERE host_id=‘354’;
DELETE FROM host_puppet_facets WHERE host_id=‘354’;
DELETE FROM host_facets_reported_data_facets WHERE host_id=‘354’;
DELETE FROM nics WHERE host_id=‘354’;
DELETE FROM reports WHERE host_id=‘354’;
DELETE FROM host_status WHERE host_id=‘354’;
DELETE FROM hosts WHERE id=‘354’;
That resolved my issue.