https://www.bleepingcomputer.com/news/microsoft/windows-10-kb4505903-update-breaks-bluetooth-speakers-connectivity/

Microsoft says that Bluetooth speakers will stop connecting to devices running Windows 10, version 1903 after installing the KB4505903 cumulative update released on July 26, 2019.

Besides the Bluetooth speakers no longer working properly, users will also notice a Microsoft Bluetooth A2dp Source entry under the Sound, video and game controllers node displaying a yellow exclamation mark icon in Device Manager.