JsonRpcTX can provide more info when commit failed. Current implementation :

final Throwable failure = new TransactionCommitFailedException(
                    "Commit of transaction " + getIdentifier() + " failed");
            listeners.forEach(txListener -> txListener.onFailure(this, failure));
            return FluentFutures.immediateFailedFluentFuture(failure);

We can instead attempt to call error RPC to get more details