 Shares of Casper Sleep Inc. tumbled 9.0 in premarket trading Monday, after the mattress-in-a-box seller reported a wider-than-expected third-quarter loss on revenue that surprisingly declined, citing supply chain challenges given as a result of the COVID-19 pandemic. The net loss narrowed to 15.9 million, or 40 cents a share, from 23.0 million, or 2.16 a share, in the year-ago period. 