Also reported here: https://community.ring.com/t5/Video-Doorbells/Black-Video-Recordings-Ring-2/td-p/4454
I just got another one on my Ring Pro, same circumstances: 40 seconds of black video. This is not an app playback issue – I see the same thing on desktop from the Ring web site – so reinstalling the app is unlikely to matter. This is not missing video, or video that stopped part way through; this is 40 seconds of black, every time.
Device Health shows RSSI -55, which is in the “sufficient” range (-65 to -41). Speed test holding my phone next to the doorbell shows 26.74 / 10.28 / 30ms.