In v8.0, the random_DDL_setFCV_operations_with_metadata_check.js test runs both moveCollection to random shards, and random setFCV operations to v7.0/v7.3/v8.0 FCV.

Since unsharded collections outside the DB primary aren't supported on FCV 7.x, if there is a downgrade while there are unsharded collections outside the DB primary, the downgrade fails with the CannotDowngrade error code.

When this happens the FCV remains at "downgrading to v7.x" transitional FCV, and the collections can't be moved back to the DB primary, since moveCollection is disabled while downgrading.

For the downgrade to v7.0 FCV, the test can easyly get out by upgrading back to v8.0 FCV via the "downgrading to upgrading" transition.

However for the downgrade to v7.3 FCV, however, no corresponding "downgrading to upgrading" transition was implemented (mainly because this downgrade is test-only, controlled by the disableTransitionFromLatestToLastContinuous parameter).

As a result, the test gets stuck once it reaches into this situation (it can only resolve is if all unsharded collections outside the DB primary get dropped).

Since v7.3 is long end-of-life the most straightforward fix is to stop testing this FCV transition.