I first looked at the image in RegiStax 6, simply trying to see why a manual channel realignment wasn't clearing thing up, but I became puzzled too. I then decided to do a channel split in Photoshop--- things became more interesting than I had expected so I had to put the attached image together.
In the R channel Io's shadow is slightly elongated along the line of dispersion--- no surprise.
The G channel shows a double shadow that is barely separated, also along the dispersion line.
The B shows a really clean and wider split of Io's shadow along the same line.
It appears that you didn't use an IR blocking filter, and so have also recorded IR leak ghost images of Io's shadow in each channel. The QE chart shows how much the IR leak is separated from each color channel, and actually some atmospheric dispersion will add a bit more too, as dispersion is greater in the shorter wavelengths. It's largely these IR ghost shadows that caused your issues when you tried to manually align the channels. A properly adjusted ADC would have merged things nicely even without an IR blocker, but for best color balance an IR block is still required.
The intersection of the tick marks on the right side indicate the location of Io, which was in transit at the time. Io has virtually no blue, and so the B image's Io is essentially completely from the IR leak and so is as sharp as it's IR shadow in that channel. In the R and G channels Io is recorded in both visible light and IR and these overlap a bit, causing a bit of blurring--- less so in the R which would be expected.
The ASI290MC is one of the ZWO color cameras that can record strong IR signal, so ZWO makes them with an A/R coated 'clear' non-blocking window so that users can choose either an IR-blocking or various IR-pass filters, giving the camera more flexibility. The good news here is that the image quality will noticeably improve just with use use of an IR blocking filter. An ADC will also help but usually takes a bit of experience to get it working just right--- you'll find yourself getting better with it with practice, and probably find yourself enjoying it for visual use too.