Why is the audio level not displayed for a few call UUIDs?

Call legs that have a PSTN number don't display the audio level. Plivo SDKs can't detect one-way audio on a PSTN leg if the audio level is too low on one of the streams. We can detect the audio level if the packet count on one of the streams is zero. If both of the streams have a packet count of zero, the call leg is labeled as “no audio.”