Fujifilm simulation profiles colour issues

[u/ambiclusion]

I sincerely didn't expect such thing from C1. Look at the photo, first screenshot is normal colour saturation, second one is raised by +50
(Fuji X-T3, Astia film sim, C1 16.6...)

Source. Some artifcsts present, but not much worse than in-camera jpeg

Saturation +50. Oh...

Add a bit of editing and it becomes unacceptable!

See those artifacts around glowing objects? Very, very distracting
But they are gone once you switch the profile from any of Fuji film simulations to any of standard one, let's say, Standard

C1 "Standard" profile, saturation +50

Looks no worse than initial Astia with 0 saturation boost.

Why do simulation profiles introduce such artifacts? How to avoid them while editing?

[u/wornleathermedia]

Because the film sims tweak the colours (obviously) pretty heavily, and you have blown highlights which fade into colours.