This happened to me and also drsteelhammer while spectating a monoset tournament match. Started out as all cards everywhere doubled except supply, then only some cards, then twice as many cards from the supply were missing as were supposed to. Second and third images have negative supplies. Third image has upside down cards appearing in weird places, which happens to me frequently when playing and spectating. I was using Firefox, drsteelhammer on Chrome. Other people speccing didn't see the bug, some of them also using Chrome or Firefox.
https://snag.gy/cNy6hK.jpg
https://snag.gy/vXWdS3.jpg
https://snag.gy/9GVTFR.jpg