In some places in the code, we have the following check of the prepared state:

      if (upd->prepare_state == WT_PREPARE_LOCKED || upd->prepare_state == WT_PREPARE_INPROGRESS)

I think this is wrong and we may see the following race condition:

1. Thread A reads the prepared state as in progress
2. Thread B marks the prepared state as locked
3. Thread A reads the prepared state again as locked and jumped out of the if section

Instead we should check the state in the opposite direction as:

      if (upd->prepare_state == WT_PREPARE_INPROGRESS || upd->prepare_state == WT_PREPARE_LOCKED)

or ensure we only read the prepared state once.