:Transposition table addition to the algorithm should not affect alpha/beta results, regardless of search depth. There are definitely errors in the implementation if it does. Having experience this too, this is particularly difficult to troubleshoot, due to recursive code, and incorrect results propagate all over the game tree quickly. Errors can be the transposition table itself, such as a table that's returning bad data, due to table entry collisions, or table corruption. Other cases are table lookup misuse (using data that should be ignored) and misinterpretation (improper save or restore of bestValue and its alpha beta relationship).