The abbreviation a2dp stands for Advanced Audio Distribution Profile. I mentioned this in the article Windows 10 V1903: Update KB4505903 breaks Bluetooth speaker connection. Note: Augwas a patchday, and Microsoft later confirmed that an update disabled Bluetooth connections. It seems as if an unsigned driver (possibly via auto-update) has broken the systems. A de- and subsequent reinstallation of the Bluetooth drivers is unlikely to help. It affects different devices, from Surface Pro 4 to HP Omen systems. In the linked MS Answers forum thread some affected persons confirmed this behavior. It is caused by a recent hardware or software change. The error message indicates that Windows cannot verify the digital signature required for the drivers. His Bluetooth A2dp source is not working properly and drops error code 52. A recent hardware or software change might have installed a file that is signed incorrectly or damaged, or that might be malicious software from an unknown source. There is error message 'Windows cannot verify the digital signature for the drivers required for this device. Microsoft Bluetooth A2dp source (error code 52) Microsoft Bluetooth A2dp source not working properly.
I encountered the problem (when writing the post a week ago) via the collection service here, the entries are from September 2019, but the better introduction is this Microsoft Answers forum thread, dated August 13, 2019, where the issue has already been discussed.
