which added stats for retransmittedBytesReceived that are exposed to Chromium as of
will also change the inbound-rtp statistics for headerBytesReceived, bytesReceived and packetsReceived slightly.
These counters now include any packets retransmitted via RTX which brings the numbers closer to the total ones than can be observed in the transport stats.
Note that bandwidth estimation probes get reported as retransmissions on the receiving end, so this counter going up is not necessarily a sign of packet loss.
If you see a slight increase in average bitrate from getStats this is likely due to this. This increase in bytesReceived should correlate with the newly added retransmittedBytesReceived.
If you are interested in the math involved please see the discussion in