A report from the BIS argues that hedge funds contributed to the spike in money markets earlier this year (emphasis added):
Shifts in repo borrowing and lending by non-bank participants may have also played a role in the repo rate spike. Market commentary suggests that, in preceding quarters, leveraged players (eg hedge funds) were increasing their demand for Treasury repos to fund arbitrage trades between cash bonds and derivatives. Since 2017, MMFs have been lending to a broader range of repo counterparties, including hedge funds, potentially obtaining higher returns.
Here's the thumbnail version: QE moved