I am a beta user of Font Awesome 6 and extensively use its desktop fonts with ligatures.
Any attempt to produce the ligature made by the string starfighter-twin-ion-engine-advanced will crash AI (26.0.2, macOS Big Sur). I believe this is a length of ligature issue as other ligatures from this typeface family are unaffected, including starfighter-twin-ion-engine, and the alias of starfighter-alt-advanced works. (Perhaps ligatures longer than 32 characters?) I was able to reproduce this twice with the aforementioned ligature and again with down-left-and-up-right-to-center (32 chars). It does not occur in Photoshop, so it is an Ai problem, not a font issue.