Somewhat related is this memo by Howard Marks that talks about the liquidity of ETFs (starts on page 6 -- the whole thing is a great read). When the market sharply drops and there is no liquidity for sellers, it might be even worse for holders of ETFs as they will have even less liquidity than the sellers of the underlying stock.

[1] https://www.oaktreecapital.com/docs/default-source/memos/201...