iPhone 7+ HDMI adapter not working after iOS 12.1.4 update

iPhone 7+ Apple branded HDMI adapter (with AC power) not working after iPhone 7+ update to iOS 12.1.4. No video or audio. It worked fine prior to the update. iPad on same OS using same adapter works fine. Tried changing screen resolution to zoom, enabled USB port for accessories. Roku TV display shows a QR code to a Drong Cast web site, drong.goodsleep.cn. Not sure what this is for. Tried downloading their drivers, none worked. It looks like a lot of folks had a similar problem, but none of the suggested answers resolved this issue for me. I don't see any recent posts about this, so I'm starting a new one. Thanks.