https://www.vice.com/en_us/article/3azeeb/tesla-and-apple-stock-split-investors-crash-robinhood-nothing-makes-sense

On Monday morning, multiple major trading platforms experienced issues processing stock trades—the same day Apple and Tesla stock splits went into effect.

A stock split is basically when a company breaks an individual share into more individual shares—breaking a $200 stock into four $50 pieces, for example. This move is usually done to make prices more attractive to "retail investors"—individual traders, not big institutional investors like universities, pensions, or hedge funds.