Hah, that might be what I already saw with G25 in nK Pro in some situations ;-)
First of all, I can't test G25 in person at the moment but I hope I will do that within this week and report back.
Ok, so here's the first thing:
G25, by design, have something to prevent backlash: two tooth wheels slightly rotated to each other, so that there should be no rattle when you don't load FF motors constantly (because those two tooth wheels will always be touching small tooth wheels from FF motors). Unfortunatelly, having a chance to took apart over dozen or more G25, not all of them have that two black wheels actually rotated. For some G25 I had for repair, I had to turn those wheels by myself, because someone in Logitech factory forgot to do that

Some of you might have that issue.
Even if you don't, those two wheels are loaded by not so stiff springs so when stronger forces load them, that anti-backlash system won't be working anymore as should. That might be the case for you guys, even that system worked OK in other sims.
As for G27 - because it use helical gears, there is no chance to have that anti-backlash system... and it doesn't have. I had G27 for myself for some time and even though it felt great overall, with better FF feeling, when I got myself over curbs of very uneven surfaces, I got sensations like with good ol' rattling Formula Force GP wheel
If I'm right, there should be no such issue on wheels like T500RS - belt driven, where there is no play between wheels teeth.