Each time you call GetBeatTrackingxxxx node the analysis is calculated for a window of time centered in the current playback time of the audio, this calculates the bpm value for the actual window (Current BPM). So, if you call it multiple times you obtain the bpm results of a lot of windows during the song.
The Total BPM counter returns the bpm value that occur most often during all the song. (The most repeated Current BPM value of all the windows).
If the song has too many “silences” for the analysis band then it can result it can increase the number of windows with a BPM value of 0, positioning the bpm-zero value as the most used by the song in that band.
You can calculate the Current BPM in different positions of the song and take the average, but in my oppinion the most repeated BPM is more exact than the average BPM.