It’s a thing that happens when a state constitution makes the quorum requirement larger than the cloture requirement, so a minority party of a certain specific size can’t filibuster by prolonging debate but it can filibuster like this, by not showing up.
It’s avoidable. Just make quorum a simple majority instead of, like, whatever it is in Oregon. Which I notice is never specifically described in any of these news articles, despite being key information to understand the story.
EDIT: From Friday’s KPFA Evening News, “Democrats have an 18 to 12 majority in the chamber, but they need 20 members present for a quorum in order to take any actions.” So the quorum requirement is ⅔ of the Senate, and this week’s events illustrate why that is too much.
