Mercedes-benz cla 45 w117

Hi I have a Mercedes CLA 45 AMG w117 When driving in auto and reaches 7th gear fault comes up P0921 on the transmission and goes into limp (reversing not possible consult work shop) usually when i get this problem change clutch flywheel and update mechatronic softwear then all good but this time sone all that but still happening what could it be check picture need advice asap stuck with vehicle until repaired