Came across this nice summary note comparing the two indices.
It is from an Indian perspective but should apply to other countries as well. The note says both are very different and hence cannot be compared:
As the methodology used for calculating IIP and PMI are different, one being based on actual production data and the other on business expectations, the comparison between the two cannot be made. The table shows that there exist no one-to-one correspondence between the two. The IIP for March decelerated to while the manufacturing PMI, however, showed expansion.
One can understand some divergence of trend on some months. But from a longer term perspective, the two indices should convey the same. If one shows contraction and other an expansion consistently, how does one make sense of the production trends?