Found the cause, that bounce is coming from ImprovMX, the service that receives mail for newsletters.newsblur.com and hands it to NewsBlur. They pushed an update on September 11 and their spam scoring now puts some WIRED emails right at the 5.0 cutoff, so the message gets rejected before it ever reaches NewsBlur. Your WIRED newsletters were arriving every day up through the 11th and then stopped, which matches. Nothing changed on your end or in NewsBlur.
I’ve asked ImprovMX to turn off spam filtering for our domain, since every newsletter address already has a secret token in it and the mail only goes to NewsBlur. I’ll update here when I hear back.