We have recently hit a failure on Atlas coming from this assertion in __wt_btcur_search_prepared (src/btree/bt_cursor.c:673), in which we did not find a key when resolving a prepared transaction:

    WT_ASSERT_ALWAYS(
      CUR2S(cursor), ret == 0, "A valid key must exist when resolving prepared updates.");

Please refer to the associated AF ticket for more information about the failure.