I resumed a race using the C6R GT2 vehicle. The gear ratio was not what I set it to use during the race, & it would reach maximum redline at 250 km/h instead of 260 km/h.
I hadn't noticed this one yet. I drive the Oreca and it doesn't allow you to change gear ratios (the latest update added a high, medium and low though). There are several things that don't work when resuming from replay. One fix for a number of those is to make your setup the default for that track. I've found that fixes several of them (fuel load, tire change) but it does not fix the mirrors returning to default position or the occasional start with pit limiter on.
How do I make the default setup for the track? This post (link), suggests to edit the .GDB file of the track, and refer to file in \rFactor 2\UserData\player\Settings\?
In the screen where you save your setups, select the setup and click Assign. You'll see it change the default setup for the track to that setup. Each time you return to the track, it will then automatically use that setup.