Okay here is a theory for comment.
What if a fund is cashing out for tax purposes because today is the end of the fiscal year?
In other words, window dressing?
If so, tomorrow or Monday they start buying it all back.
If this is true and they are on the West Coast of US, then the dumping will stop in about a half hour.
In the US, companies can select whatever fiscal year they want for accounting purposes (i.e. for audited financials and SEC filings), but the IRS taxes everyone on a calendar year basis.
That said, deadline for filing tax returns, if you got an extension, is Oct 15. But that is for personal tax returns. Corporate tax return extension deadline was Sep 15. [Edit - to clarify, this could cause some selling pressure, but not much. When you elect an extension in April, you have to pay estimated taxes at that time. So the only people dumping bitcoin for US tax purposes now would be people who were smart enough to realized they would owe taxes on bitcoin and file an extension, but not smart enough to pay their estimated taxes at that time and thus face penalties.]
In the stock market, there is a "window dressing" effect where funds may play games at the end of a quarter - piling into hot stocks, dumping weak ones. That way, they can say they owned those companies in their quarterly filings.