Oh, that's right - I saw Vanguard glitching near the market open. Normally the brokerage screen has updated values of all ETFs after the market opens - they had values from the prior day. When I went to the buy screen, I got correct info. I waited several seconds, reloaded... did that once or twice.
Then every ETF I own had "--" listed for it's price, change and everything. No data at all. It was very odd, but I wasn't in a rush to send in transactions when that's happening. So I logged out, and got back to it later.
What's especially puzzling is that Vanguard held up fine on Monday, March 9. I sent in limit orders to execute at the market open, and they did. I did some ill-advised purchases in the first 3 minutes of the day, before trading halted. All of that happened smoothly. I'm not sure what was up Wednesday morning (EST) of March 18.