From plenty of experience with other DX12 games that do proper shader pre-compilations when you first load up the game, driver updates wipe out this built up shader cache and force these processes to start all over again. These are usually long, and can take 5-15 minutes or more and really stress the CPU while it's happening.
WRC doesn't have anything like that, and appears to use UE4's PSO for compiling shaders when loading stages (stage loads seem longer now than at release, but initial boot time doesn't seem any slower), but this brief pre-compile of shaders still doesn't cover every possible shader in the game or even in that stage in the moment. So every time you update your drivers, you will experience a little more stuttering again as these missed shaders are cached on the fly. It will smooth out over time, same as it did at launch, but with fewer stutters overall since they are pre-compiling some of them, just not all.
Rolling back your drivers will not help, sorry to say. Only thing that would help this situation is if Codemasters/EA were to code a custom full shader pre-compilation of absolutely everything in the game, or migrate over to UE5 in the future if they ever make it easier/better in that engine version to compile all shaders. Apparently UE4 does not make it easy, the developer of Hi-Fi Rush has talked about the extra work they had to do to eliminate the shader stutter in their game.
While that game was one of the smoothest modern UE4+DX12 releases I played, the interview points out they still couldn't resolve every single stutter stemming from UE4 "In Hi-Fi Rush, some hitches remain, but they are mostly during certain cutscene transitions that don’t affect gameplay" - a fast paced racing game like WRC obviously doesn't have the luxury there.
