In Revit 2019 new functionality was introduced called 'double fill patterns'. This new function gives you the ability to apply two fill patterns to a cut or surface pattern. For example, a brick hatch over a solid colour. This example is from the Autodesk knowledge network page:
Today I noticed using foreground or background fill pattern has an impact on the visibility graphics when used with detail level.
In the example below, I have set two filters; one using foreground solid cut pattern, the other a background solid cut pattern. (The filters reference different values in the comments). I have duplicated the views and assigned different detail levels. As you can see, if your detail level is set to 'course' any background fill pattern overrides do not display.
It's worth noting, even when I tried with an element override, I got the same result. If you apply both foreground and background patterns, then the background pattern displays regardless of detail level.