Hi Ninabean,
looks like you are facing NIM011332: Zooming into a small scale causes BMP marker fill symbology to disappear.
The picture marker fill symbology will not print, export, or display in ArcMap when the data is zoomed to a very large scale.
You could try if the symbol looks better when converting it to *.emf (or *.jpg, *.png, *.tif when using ArcGIS 10.2.x).
For some symbols, you will find multiple graphic files available for your use in the ArcGIS Pictures folder already. Since these may be scaled differently, you can choose the one that best works for the scale of your map.
Within a small test it helped on my machine to export the symbol once again into a style and "re-use" that symbol. But that is unfortunately not an 100% solution.... it is not helping every symbol.
Hope these information help you,
Anna
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Technical Support Esri Germany