Missing images and background-pdfs from PDF while viewed in Adobe Acrobat and Acrobat Reader

After a bit of research in this forum I found there are many problems regarding missing images from a PDF.

We are producing PDFs for emailings. When opening the PDF in Adobe Acrobat or Reader there are many images missing. In MS Edge everything is displayed.

Difficult to debug because:

• "Show transparency grid" causes images to appear or disappear.
• Different PDF viewers deliver different results (MS Edge is okay, Acrobat is not okay).
• Opening the "Output Preview" window also changes results, even without changing any settings.
• Furthermore, in the "Output Preview" the representation changes when you select "Simulate Black Ink," but only if you are not on the affected page.

For example, when you are on page 2, you change settings and nothing happens. (Showing works, but hiding back does not.) So you revert the settings. However, if you move away from the recently viewed page, e.g., to page 3, and then change the settings, you find upon returning to page 2  an empty page.

Does anybody have any ideo on how to approach this?
What would be steps I could try?
I am thankful for every idea!

Best regards,

BASti