Thanks for your reply. Sorry for skipping relevant infos, my bad.
- CMS Pages > Page "XY Account" has Page Type "Product Bank Account"
- "Product Bank Account" inherits "Product Extended" which inherits "XY.Product" and
- finally PageType "XY.Product" represents a product type (accourding to E-commerce config element)
That's the reason why we expect fields from SKU.Product to be shown on form Tab in Pages application.
This was working before and is still working on QA environment!
We have been checking for alternative forms but we don't use them either.
Any other ideas what to look into?