Forex What caused this large gap on the EURUSD monthly chart?

Shamefully, I'm not particularly educated on what price gaps signify. I do however, know that they appear when price makes an extremely sharp move - often outside of market hours - which means that the open and close do not align as they should.

On, daily charts and below - I assume that gaps may commonly exist due to changes in price over the weekend. However, moving up to the monthly timeframe, gaps (as you would expect) become far less common.

This leads me to wonder what could possibly have caused such a large gap on the monthly timeframe here...?

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