Sometimes fail when copying/deleting multiple lists

All the list copy/deletions are done in parallel, so this is likely a race condition ~~as it's pretty rare to occur~~ that occurs roughly 1/3 of the time when done for 5+ lists.

Start by locating the code that performs list copy and deletion in parallel, then reproduce the failure with 5 or more lists. The issue is resolved when repeated multi-list copy and deletion operations no longer fail intermittently.

Written by the indexing model from the issue text.