"If you look at line 1038, it checks if the interval mode is set to ‘aux’. If it is, it calculates a new interval, but skips the ‘runIntervalHdrCheck’ function on line 1045, which is run if the interval is triggered internally. This is the function that sets the timing for the next photo in an HDR sequence."
HDR feature does not work with aux input.
Per email discussion with James:
https://github.com/timelapseplus/VIEW/blob/master/intervalometer/intervalometer.js
"If you look at line 1038, it checks if the interval mode is set to ‘aux’. If it is, it calculates a new interval, but skips the ‘runIntervalHdrCheck’ function on line 1045, which is run if the interval is triggered internally. This is the function that sets the timing for the next photo in an HDR sequence."