I just had a look in the INI files to see what may have changed, here is one thing I noticed is different to how it used to be in earlier builds. Here is the Assetto_Corsa.ini as loaded by default, I double checked by doing a steam verify and this is how the file ends up.
[ASSETTO_CORSA]
SLEEP_TIME=-1
WARNINGS_AS_ERRORS=0
[FORCE_FEEDBACK]
MAX_FF_RATE_HZ=333
[AC_APPS]
ENABLE_DEV_APPS=0
[TELEMETRY]
EXPORT_ENTIRE_SESSION=1
[SCREENSHOT]
FORMAT=JPG
[TIME_DIFFERENCE]
POS_Y=200
[THREADING]
USE_TIMER_PROCESS=-1 ; -1=Automatic, no timer process for CPU with more than 2 cores, timer process for dual cores. 0=Always off. 1=Always on.
SET_THREAD_AFFINITY_MASK=0 ; 0=Windows scheduler will decide where to run the threads. 1=Main thread assigned to Core0, physics thread assigned to Core1
[AUDIO]
MAX_CHANNELS=64
SURFACES_DISTANCE_SCALE=2
UPDATE_INTERVAL=16
DISABLE_ENGINE_SOUNDS=0
[RACE]
OVER_TIME_MULT=1.2
[DEBUG]
MULTI_LOG=0
PHYSICS_TIME_SCALE=1
[DIRT]
MULT=1
[VIRTUAL_MIRROR]
ACTIVE=1
[DAMAGE]
GLASS_THRESHOLD=0.65
[DRIVER]
HIDE=0
[CAMERA]
ALLOW_FREE_CAMERA=1
I remember in earlier builds Telemetry export entire session was default at 0. I did try it at 1 back then and got much worse performance, for me as it is currently runs fine but maybe for others its worth trying this at =0 and see if it improves things.
