Fixed background images not showing up in some tablet / phone devices

Hello,
I set up some fixed background images on several pages of a website and on all the devices in my office everything looks and works well (PC, laptop, and tablets. I "hid" these sections in the Phone settings). On my clients devices however (two tablets and two laptops) all the fixed images do not show at all. I changed the setting to scroll and now it is visually working, but not as impressive. What would cause this issue? One of the tablets is brand new, but her other devices are older.

Thank you!

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