Could be a number of reasons. Were the bloated stars only the brightest ones, this could just mean over exposure. Patchy high cloud that was undetectable with the naked eye could have been causing bloated stars. Bad seeing conditions? etc. I notice you have a tremendous amount of Ha showing, were you using an Ha filter with a modded camera? Was your Ha shot taken separate from your RGB? Quite often when you merge your Ha data with RGB data, the brighter stars can appear bloated. Just a few thoughts.
Nice photo by the way, I have done some Nightscapes from that very location myself.
