it wasn't that they were halted, they just hadn't opened yet and the etf didn't know how to price them. It probably happens every single morning, but the mispricing is so small no one bothers to notice. Maybe an etf shouldn't trade until all it's underlyings are open.
No one's mentioned the create/redeem process Which is how you price etfs. You don't need the entire constituents to arb but the underlyings were less liquid than the etf