How to make moveable platform not affect character speed?

In the Endless Runner YouTube series, part 7 wrap up, Rob shows his more polished prototype around 4:15 into the video. Almost immediately you see him run over a floor trigger which extends a bridge. I’ve reproduced this effect perfectly fine but with a caveat I don’t want: it speeds up my character while the bridge is moving under me. Sometimes a lot. I could make the bridge interp faster so it’s done moving by the time I first step on it but I don’t want to; that’d be too “instant.”

I’ve tried changing various collision/physics settings but I admit I’m not quite sure what I’m doing; either way, nothing has worked. I could also probably spawn a static blocking volume over top of where the bridge will eventually be but that feels hackish to me and may have consequences in the future (may block things I didn’t want it to like fireballs or something).

Is there a magic setting/checkbox I’m overlooking?