Can you show volume for this bar? Is it unusually high?
I would not say Oanda did this… Thing is - markets are unpredictable and spikes appear a lot. Your trade got busted in a range with high volatility - that happens.
Each broker has its own order book - there can be single spikes on one broker. There are multiple algorithms running on each broker. The spike can be caused by as trivial thing as robot issue in some bank or individual. Keep in mind, that GBP/NZD is not the most liquid pair - this also may contribute to differences between brokers. It’s hard to imagine to have such discrepancy between brokers for EURUSD.
My broker reached 1.965 on 6th Oct