With enable-majority-read-concern false (EMRC=false), we may have a failure during rollback, when the rollback source was on a branch of history which is ultimately rolled back itself. This results in the minValid document on the failed node being on the wrong branch of history. If no sync source still has this branch of history, the situation is unrecoverable, but we do not detect this.

It's not 100% clear how we would; we could see if no nodes had the requiredOpTime and if so declare it unrecoverable, but this wouldn't solve the BF because one node was unreachable at the time.