Get access to VCDS (VCDS register on this forum) and check block 90 for the actual and specified adjustment. The actual adjustment should be within + or - 1 kw of the specified adjustment. So if the specified adjustment is 24kw you want to see 23-25kw in the actual adjustment. If all is in order as described as above then the problem isnt in the cam chain change... something seperate.
As said, the hpfp is removed from its cover, and then the cover itself is removed during the chain change so it is possible that something in the process has caused the issue. I think that one of the electrical sensors on the hpfp itself is damaged/failed. Check them