If a summary row has a subtable, it will not be serialized because we go over the
$rows property, but the summary row is held in a different property. Fixed by including it.
This was causing the strange "Row with label '%s' (columns = %s) has already a subtable" errors. The summary row subtable couldn't be loaded from the DB, just the ID, so when summing them, we'd trigger this warning.
As I see in the tests there is an error.
The test failure seems unrelated. This is for an L3 issue in JIRA so the description of the bug it fixes is hidden, and it would be pretty hard to manually test. You'd have to set the ranking query INI config really low, track a ton of data w/, say, events that creates top level reports w/ subtables (including in the Others row), then archive w/ ranking query. I couldn't actually get that to work, so just debugged on prod.