Taking "in progress" to the next level.

[Canadane]

CAN, but doesn't always, and that's the problem. I tried to help out an FC-mate just last week who'd had their tank D/C or bail or something in Titan Trial mode. I didn't Low Roulette - I signed up directly for Titan Trial Mode. Poof, I wind up in a newly-formed group. My FC-mate thanks me for trying, and his group disbands shortly afterwards.

This simply should not happen. It makes no sense.

That may have been because the party leader didn't end up recruiting replacements. It may have been that they were preformed and didn't realize you can't get a drop-in rep if you start out as preformed.
In my experience it would always put me in an in-progress queue before a new party if there's one with an option recruiting slot for my role.