Since October 1st GA only tracks 10-20% of users and sessions. The conversion discrepancy seems to be consistently be 10% lower for GA.
We did not change anything, nor has there been a major update. We reviewed the implementation various times and checked that the tags are firing on the Google Tag Assistant. We thought maybe our user consent management platform is somehow at fault, but this was also a miss. It's all a mystery.
It's starting to really affect our Google Ad CPA since the data for optimization is not passed on properly anymore.