The following places use the

if (failpoint) {
    while (failpoint) {
        sleepsecs(1)
    }
}

pattern, without checking for shutdown inside the while:

SyncTail::getMissingDoc()
https://github.com/mongodb/mongo/blob/d9d8ac1e8ae85a07369274eaf12c0ce555e08b2e/src/mongo/db/repl/sync_tail.cpp#L948-L954

rs_rollback.cpp::_syncRollback()
https://github.com/mongodb/mongo/blob/d9d8ac1e8ae85a07369274eaf12c0ce555e08b2e/src/mongo/db/repl/rs_rollback.cpp#L912-L919

CollectionCloner::_insertDocumentsCallback
https://github.com/mongodb/mongo/blob/d9d8ac1e8ae85a07369274eaf12c0ce555e08b2e/src/mongo/db/repl/collection_cloner.cpp#L496-L506

rs_initialsync.cpp::_initialSync
https://github.com/mongodb/mongo/blob/d9d8ac1e8ae85a07369274eaf12c0ce555e08b2e/src/mongo/db/repl/rs_initialsync.cpp#L310-L316

Cloner()
https://github.com/mongodb/mongo/blob/d9d8ac1e8ae85a07369274eaf12c0ce555e08b2e/src/mongo/db/cloner.cpp#L285-L295

If some test turns on the failpoint but forgets to turn it off, a node that hits the failpoint will hang in shutdown, causing failures like the ones addressed by SERVER-26928.

They should all be changed to check for being in shutdown (possibly through the inShutdown() function).