Like most computer issues, rebooting fixed it. I'm running 3 displays through a DP splitter through a TB3 dock :-) The laptop, splitter, and dock are all DP 1.4, and dock supports dual 4k 60Hz through a single DP port, so I thought it could run three 1920x1920 at 60Hz, but I can only get two at 60Hz and the third at 30Hz. That should be fine for my use. Annoying: it only works on the laptop's right TB3 port, not the left TB3 port. Oh well.