What causes any particular currency pair to move at market open/crossover between sessions?

In the FX market, at market open/crossover between sessions often larger moves are observed within currency pairs. In reality, what exactly causes these moves? Is it institutional positions being opened or closed for the session? I can hardly imagine that retail traders make a dent in the graph movement. Know it’s not a straightforward question to answer, but would love to hear some of your opinions and views?

Yes its the bog players. In forex, the total positions of private retail traders are invisibly small.

Yes, they are invisibly small. It’s true.

Usually at market open European and USA - very often numbers are released at these times.

Market close is often muted.