Running a simple sample of Testbox code fails with java.util.ConcurrentModificationException in StructClear().
Locking (either scope or name locks) doesn't seem to do anything.
Now - one can argue that this code might be not great, but it works just fine in ACF.
Linux (Ubuntu 18.04) via Command Box 4.8.0
Same issue also happens in Luce 5.2.9