Why is there an echo when using ffmpeg's amix to stream to SRS?

[191474639]

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Describe the bug
Combine multiple RTMP streams from several SRS (Simple Real-time Streaming Service) sources, and upon playback, the audio is repeated several times.
Version
6.0

To Reproduce
Steps to reproduce the behavior:
Using a command
ffmpeg -i rtmp://36.1.X.XX/live/aaaaa -i rtmp://36.1.X.XX/live/mvp -c:v libx264 -filter_complex "[0][1]amix=inputs=2:duration=first:dropout_transition=3[a]" -map 0:v -map "[a]" -rtmp_buffer 500 -probesize 32M -analyzeduration 5M -vsync 2 -c:a aac -f flv rtmp://36.1.X.XX/live/merge1
Expected behavior
A clear and concise description of what you expected to happen.

Screenshots

Additional context
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