ok, we noticed serious less orders the last 2 weeks.
We started checking products and noticed that on 10 percent of our products PPOM Meta had been removed from the products.
We had to go one by one checking and relink ppom meta data.
We noticed that indeed, as stated above, the linked PPOM would not show correct in edit product and when saving the data, PPOM is removed completely.
This caused us some serious problems.